bgpd: fix as-path exclude modify crash

[ton31337]

Fix a crash when modifying a route-map with set as-path exclude without as-path-access-list:

router(config)# route-map routemaptest deny 1
router(config-route-map)# set as-path exclude 33 34 35
router(config-route-map)# set as-path exclude as-path-access-list test

#0 raise (sig=) at ../sysdeps/unix/sysv/linux/raise.c:50
#1 0x00007fb3959327de in core_handler (signo=11, siginfo=0x7ffd122da530, context=0x7ffd122da400) at lib/sigevent.c:258
#2
#3 0x000055ab2762a1bd in as_list_list_del (h=0x55ab27897680 <as_exclude_list_orphan>, item=0x55ab28204e20) at ./bgpd/bgp_aspath.h:77
#4 0x000055ab2762d1a8 in as_exclude_remove_orphan (ase=0x55ab28204e20) at bgpd/bgp_aspath.c:1574
#5 0x000055ab27550538 in route_aspath_exclude_free (rule=0x55ab28204e20) at bgpd/bgp_routemap.c:2366
#6 0x00007fb39591f00c in route_map_rule_delete (list=0x55ab28203498, rule=0x55ab28204170) at lib/routemap.c:1357
#7 0x00007fb39591f87c in route_map_add_set (index=0x55ab28203460, set_name=0x55ab276ad2aa "as-path exclude", set_arg=0x55ab281e4f70 "as-path-access-list test") at lib/routemap.c:1674
#8 0x00007fb39591d3f3 in generic_set_add (index=0x55ab28203460, command=0x55ab276ad2aa "as-path exclude", arg=0x55ab281e4f70 "as-path-access-list test", errmsg=0x7ffd122db870 "",
errmsg_len=8192) at lib/routemap.c:533
#9 0x000055ab2755e78e in lib_route_map_entry_set_action_rmap_set_action_exclude_as_path_modify (args=0x7ffd122db290) at bgpd/bgp_routemap_nb_config.c:2427
#10 0x00007fb3958fe417 in nb_callback_modify (context=0x55ab28205aa0, nb_node=0x55ab27cb31e0, event=NB_EV_APPLY, dnode=0x55ab28202690, resource=0x55ab27c32148, errmsg=0x7ffd122db870 "",
errmsg_len=8192) at lib/northbound.c:1538
#11 0x00007fb3958ff0ab in nb_callback_configuration (context=0x55ab28205aa0, event=NB_EV_APPLY, change=0x55ab27c32110, errmsg=0x7ffd122db870 "", errmsg_len=8192) at lib/northbound.c:1888
#12 0x00007fb3958ff5e4 in nb_transaction_process (event=NB_EV_APPLY, transaction=0x55ab28205aa0, errmsg=0x7ffd122db870 "", errmsg_len=8192) at lib/northbound.c:2016
#13 0x00007fb3958fddba in nb_candidate_commit_apply (transaction=0x55ab28205aa0, save_transaction=true, transaction_id=0x0, errmsg=0x7ffd122db870 "", errmsg_len=8192)
at lib/northbound.c:1356
#14 0x00007fb3958fdef0 in nb_candidate_commit (context=..., candidate=0x55ab27c2c9a0, save_transaction=true, comment=0x0, transaction_id=0x0, errmsg=0x7ffd122db870 "", errmsg_len=8192)
at lib/northbound.c:1389
#15 0x00007fb3959045ba in nb_cli_classic_commit (vty=0x55ab281f6680) at lib/northbound_cli.c:57
#16 0x00007fb395904b5a in nb_cli_apply_changes_internal (vty=0x55ab281f6680, xpath_base=0x7ffd122dfd10 "/frr-route-map:lib/route-map[name='routemaptest']/entry[sequence='1']",
clear_pending=false) at lib/northbound_cli.c:184
#17 0x00007fb395904ebf in nb_cli_apply_changes (vty=0x55ab281f6680, xpath_base_fmt=0x0) at lib/northbound_cli.c:240
--Type for more, q to quit, c to continue without paging--
#18 0x000055ab27557d2e in set_aspath_exclude_access_list_magic (self=0x55ab2775c300 <set_aspath_exclude_access_list_cmd>, vty=0x55ab281f6680, argc=5, argv=0x55ab28204c80,
as_path_filter_name=0x55ab28202040 "test") at bgpd/bgp_routemap.c:6397
#19 0x000055ab2754bdea in set_aspath_exclude_access_list (self=0x55ab2775c300 <set_aspath_exclude_access_list_cmd>, vty=0x55ab281f6680, argc=5, argv=0x55ab28204c80)
at ./bgpd/bgp_routemap_clippy.c:856
#20 0x00007fb39589435d in cmd_execute_command_real (vline=0x55ab281e61f0, vty=0x55ab281f6680, cmd=0x0, up_level=0) at lib/command.c:1003
#21 0x00007fb3958944be in cmd_execute_command (vline=0x55ab281e61f0, vty=0x55ab281f6680, cmd=0x0, vtysh=0) at lib/command.c:1062
#22 0x00007fb395894a0c in cmd_execute (vty=0x55ab281f6680, cmd=0x55ab28200f20 "set as-path exclude as-path-access-list test", matched=0x0, vtysh=0) at lib/command.c:1228
#23 0x00007fb39595242c in vty_command (vty=0x55ab281f6680, buf=0x55ab28200f20 "set as-path exclude as-path-access-list test") at lib/vty.c:625
#24 0x00007fb3959541c5 in vty_execute (vty=0x55ab281f6680) at lib/vty.c:1388
#25 0x00007fb3959563db in vtysh_read (thread=0x7ffd122e2bb0) at lib/vty.c:2400
#26 0x00007fb39594b785 in event_call (thread=0x7ffd122e2bb0) at lib/event.c:1996
#27 0x00007fb3958d1365 in frr_run (master=0x55ab27b56d70) at lib/libfrr.c:1231
#28 0x000055ab2747f1cc in main (argc=3, argv=0x7ffd122e2e08) at bgpd/bgp_main.c:555

Fixes: 094dcc3 ("bgpd: fix "bgp as-pah access-list" with "set aspath exclude" set/unset issues")