Audit: collect sessionid in netlink messages

Previously I added sessionid output to all audit messages where it was
available but we still didn't know the sessionid of the sender of
netlink messages.  This patch adds that information to netlink messages
so we can audit who sent netlink messages.

Signed-off-by: Eric Paris <eparis@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/include/linux/netlink.h b/include/linux/netlink.h
index fb0713b..bec1062 100644
--- a/include/linux/netlink.h
+++ b/include/linux/netlink.h
@@ -166,6 +166,7 @@
 	__u32			dst_group;
 	kernel_cap_t		eff_cap;
 	__u32			loginuid;	/* Login (audit) uid */
+	__u32			sessionid;	/* Session id (audit) */
 	__u32			sid;		/* SELinux security id */
 };