zebra: MBGP routes should not be installed in the kernel

zebra: MBGP routes should not be installed in the kernel

MBGP routes are used only for PIM RPF checks and hence should
not be installed in the kernel's FIB. Ignore route node set to Multicast
SAFI.

Signed-off-by: Balaji.G <balajig81@gmail.com>
Acked-by: Everton Marques <everton.marques@gmail.com>
[pushed down rn->table->info assignment below assert]
Signed-off-by: David Lamparter <equinox@opensourcerouting.org>
(cherry picked from commit 9511633e08ff15c23608983fdc1bc735d427332e)

Conflicts:
	zebra/zebra_rib.c