zebra: add vtep_ip to rmac nh_list in all cases

zebra: add vtep_ip to rmac nh_list in all cases

zebra rmac has a nh_list which tracks the assigned VTEP IPs to RMACs.
It can also receive IPv6 encoded IPv4 addresses as VTEPs. Changing/
Installing the RMAC into the Kernel is only important when the IPv4
address changes. However because nh_list is a nodup list used to
track usage or RMACs by VTEP IPs, both IP addresses (IPv4 and IPv6
encoded IPv4) should be written into it, as both could be removed
in l3vni_rmac_nh_list_nh_delete independently.

Signed-off-by: Christopher Dziomba <christopher.dziomba@telekom.de>