[submodule]: update sonic-swss

* 6e76e9b 2018-10-22 | [vstest]: fix redis mount point with --dvsname option (sonic-net#654) (HEAD, origin/master, origin/HEAD) [lguohan]
* 3d4bed1 2018-10-22 | [mirrororch]: Fix bug when no need to update session type (sonic-net#648) [Shuotian Cheng]
*   4bf28ed 2018-10-22 | Merge pull request sonic-net#649 from lguohan/vstest [lguohan]
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| * 8620a51 2018-10-22 | [vstest]: disable ipv6 in test_crm.py::test_CrmFdbEntry [Guohan Lu]
| * f684d65 2018-10-21 | change mode to 644 for test_setro.py [Guohan Lu]
| * 51e0d40 2018-10-22 | Enable aclfield.data for SAI_DTEL_ATTR_INT_L4_DSCP [Guohan Lu]
| * 9290950 2018-10-21 | use unique directory to mount redis.sock [Guohan Lu]
| * 7d1b09e 2018-10-21 | add --keeptb option to keep testbed after test [Guohan Lu]
| * 6ee779c 2018-10-22 | gather logs from vs container [Guohan Lu]
| * 9b49555 2018-10-21 | make sure delete the srv namespace after test [Guohan Lu]
| * e04bd2d 2018-10-20 | add testlog for all tests [Guohan Lu]
| * a2d9be4 2018-10-20 | simplify start_swss/stop_swss [Guohan Lu]
| * d76a560 2018-10-21 | add ingore object type to CountSubscribedObjects [Guohan Lu]
| * 5e2c1de 2018-10-20 | refactor test_swss_neighbor_syncup test [Guohan Lu]
| * 9e9a553 2018-10-20 | ensure vrfmgrd, teammgrd, portmgrd are running before test [Guohan Lu]
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* e8e3ddc 2018-10-21 | disable ipv6 for vEthernet interface in virtual switch (sonic-net#650) [lguohan]
* 7c90bb3 2018-10-19 | Fix portorch bake: get port count from db (sonic-net#645) [Qi Luo]

Signed-off-by: Guohan Lu <gulv@microsoft.com>