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/net/netlabel.h b/include/net/netlabel.h
index 5e53a85..e4d2d6b 100644
--- a/include/net/netlabel.h
+++ b/include/net/netlabel.h
@@ -103,6 +103,7 @@
 struct netlbl_audit {
 	u32 secid;
 	uid_t loginuid;
+	u32 sessionid;
 };
 
 /*