This command is missing.

Fixes: 5c79de6e ("[XFRM]: User interface for handling XFRM_MSG_MIGRATE")
Reported-by: NStephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: NNicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>