[Glossary] Add glossary references to networking-sfc guide
[Glossary] Add glossary references to networking-sfc guide

Add SFC, PBR, SDN, OVS, NSH to glossary.

Change-Id: I1fbec0d5ff439603def21eb384fb3d9709a8f8c4
Partial-Bug: #1605684

openstack/openstack-manuals,openstack/openstack-manuals,openstack/openstack-manuals,openstack/openstack-manuals