openvswitch: Export lockdep_ovsl_is_held to modules.

ERROR: "lockdep_ovsl_is_held" [net/openvswitch/vport-gre.ko] undefined!

Reported-by: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/openvswitch/datapath.c b/net/openvswitch/datapath.c
index aecddb9..f18302f 100644
--- a/net/openvswitch/datapath.c
+++ b/net/openvswitch/datapath.c
@@ -131,6 +131,7 @@
 	else
 		return 1;
 }
+EXPORT_SYMBOL(lockdep_ovsl_is_held);
 #endif
 
 static struct vport *new_vport(const struct vport_parms *);