zebra: rt_socket.c should not use SET_FLAG

zebra: rt_socket.c should not use SET_FLAG

The SET_FLAG(nexthop->flags, NEXTHOP_FLAG_FIB)
is already taken care of in zebra_rib.c.  There
is no need for this to be handled by rt_socket.c.

rt_netlink.c does not do a SET_FLAG(nexthop->flags, NEXTHOP_FLAG_FIB)
for route installation.  Please note it does do it for a mpls
labeled route installation, which will be fixed in a future
commit.

Remove some dead code from 2002 as well.

Signed-off-by: Donald Sharp <sharpd@cumulusnetworks.com>