lib, zebra, vtysh: configure an interface in non-default VRF

Introduce a new command "interface IFNAME vrf N" to configure an
interface in the non-default VRF.

Till now, only zebra uses this command. Other daemons will install
the command when they support multiple VRFs.

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>
diff --git a/vtysh/extract.pl.in b/vtysh/extract.pl.in
index 99d80ed..f057e24 100755
--- a/vtysh/extract.pl.in
+++ b/vtysh/extract.pl.in
@@ -31,6 +31,7 @@
 EOF
 
 $ignore{'"interface IFNAME"'} = "ignore";
+$ignore{'"interface IFNAME " "vrf <0-65535>"'} = "ignore";
 $ignore{'"ip vrf NAME"'} = "ignore";
 $ignore{'"router rip"'} = "ignore";
 $ignore{'"router ripng"'} = "ignore";