ipv6: propagate genlmsg_reply return code

genlmsg_reply can fail, so propagate its return code

Fixes: 915d7e5e ("ipv6: sr: add code base for control plane support of SR-IPv6")
Signed-off-by: Li RongQing <lirongqing@baidu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>