bgpd: Incorrect sent prefix count for a split subgroup

bgpd: Incorrect sent prefix count for a split subgroup

When a subgroup splits to form a new subgroup because of policy changes
for a peer, new subgroup copies adj out(state about advertised routes)
from the parent subgroup. At the same time, it should also copy
scount(advertised prefix count) to the new subgroup for the count to be
in sync with the adj_out for the subgroup.

Signed-off-by: Ameya Dharkar <adharkar@vmware.org>