bgp: T6473: missing completion helper for peer-groups inside a VRF
Using BGP peer-groups inside a VRF instance will make use if the global VRFs
peer-group list during tab-completion and not the peer-groups defined within
the BGP instance of the given VRF.
(cherry picked from commit 80ea3d53b2224676d3e9287bce80df4407fe6c01)