selinux/nlmsg: add XFRM_MSG_REPORT

This command is missing.

Fixes: 97a64b45 ("[XFRM]: Introduce XFRM_MSG_REPORT.")
Reported-by: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>