xfrm: Export symbol xfrm_dev_state_delete.

This fixes a build failure if xfrm_user is build as a module.

Fixes: 07b87f9e ("xfrm: Fix unregister netdevice hang on hardware offload.")
Reported-by: Mark Brown <broonie@kernel.org>
Tested-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

net/xfrm/xfrm_state.c

@@ -698,6 +698,7 @@ void xfrm_dev_state_delete(struct xfrm_state *x)
 		spin_unlock_bh(&xfrm_state_dev_gc_lock);
 	}
 }
+EXPORT_SYMBOL_GPL(xfrm_dev_state_delete);
 
 void xfrm_dev_state_free(struct xfrm_state *x)
 {