openvswitch: Export lockdep_ovsl_is_held to modules.

ERROR: "lockdep_ovsl_is_held" [net/openvswitch/vport-gre.ko] undefined!
Reported-by: NAlexei Starovoitov <alexei.starovoitov@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/openvswitch/datapath.c

@@ -131,6 +131,7 @@ int lockdep_ovsl_is_held(void)
 	else
 		return 1;
 }
+EXPORT_SYMBOL(lockdep_ovsl_is_held);
 #endif
 
 static struct vport *new_vport(const struct vport_parms *);