xfrm_policy: Do not attempt to deleteall a socket policy

Socket polices are added to a socket using setsockopt(2). They cannot be
deleted by iproute2. The attempt to delete them causes an error
(EINVAL).
To avoid this unnecessary error message all socket policies are skipped
in xfrm_policy_keep.

Signed-off-by: Thomas Egerer <thomas.egerer@secunet.com>

ip/xfrm_policy.c

@@ -735,6 +735,10 @@ static int xfrm_policy_keep(const struct sockaddr_nl *who,
 	if (!xfrm_policy_filter_match(xpinfo, ptype))
 		return 0;
 
+	/* can't delete socket policies */
+	if (xpinfo->dir >= XFRM_POLICY_MAX)
+		return 0;
+
 	if (xb->offset + NLMSG_LENGTH(sizeof(*xpid)) > xb->size)
 		return 0;