Multiple next-hop self config stanzas generate a list

[mirceaulinic]

For example, for the following policy:

luca@bsr1.atl2> show configuration policy-options policy-statement INTERNAL-ATL2-RR-OUT
term LOCAL-BE {
    from {
        protocol static;
        community PACKET-BE;
    }
    then {
        local-preference 500;
        next-hop self;
        accept;
    }
}
term LOCAL-PUBLIC {
    from {
        protocol static;
        prefix-list ANNOUNCE-ATL2-V4;
    }
    then {
        local-preference 500;
        next-hop self;
        accept;
    }
}
term LOCAL-CUSTOMERS {
    from {
        protocol bgp;
        community PACKET-ATL2-CUSTOMER;
        route-filter 0.0.0.0/0 upto /24;
    }
    then {
        next-hop self;
        accept;
    }
}
term GLOBAL-IP {
    from {
        protocol bgp;
        community PACKET-ATL2-GLOBAL-IP;
    }
    then {
        next-hop self;
        accept;
    }
}
term EVPN-REJECT-DEFAULT {
    from {
        protocol evpn;
        route-filter 0.0.0.0/0 exact;
    }
    then reject;
}
term EVPN-PACKET-INTERNAL {
    from {
        family evpn;
        community PACKET-INTERNAL-RT;
    }
    then accept;
}
then reject;

nhs_policies[p] would be a list: [True, True, True, True].

Therefore, in case nhs_policies[p] is a list, then there's at least
one next-hop self knob configured in the policy, so it can be marked as
NHS-type policy.

[coveralls]

Coverage increased (+0.002%) to 81.103% when pulling eff855f on issue-1359 into 036ddc3 on develop.