ospf6d, bgpd: avoid calling if_nametoindex

ospf6d, bgpd: avoid calling if_nametoindex

As the comments in if.h, it is better to call ifname2ifindex()
instead of if_nametoindex().

And ifname2ifindex() can work for VRF by appending a parameter
while if_nametoindex() can not.

Signed-off-by: Feng Lu <lu.feng@6wind.com>
Reviewed-by: Alain Ritoux <alain.ritoux@6wind.com>
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Acked-by: Vincent JARDIN <vincent.jardin@6wind.com>
Signed-off-by: David Lamparter <equinox@opensourcerouting.org>
(cherry picked from commit 395828eea809e8b2b8c5824d3639cefedd7aa9f0)