bgpd: fix vpn import from local vrf with no retain

bgpd: fix vpn import from local vrf with no retain

The BGP "no retain" VPN option avoids storing VPN prefixes that are not
imported in the incoming BGP table (aka. Adj RIB in). When a VPN import
policy is changed, BGP does a soft clear so that a prefix refresh is
requested from the peers. However, the import from local VPN prefixes
is never requested.

Fix this issue by requesting a local import refresh.

Fixes: a486300b26 ("bgpd: implement retain route-target all behaviour")
Signed-off-by: Louis Scalbert <louis.scalbert@6wind.com>