Fix a pointer size error in test_bridges.c

sizeof(ret) is the size of the pointer, not the size of what it
points to.  Fortunately, we already have a function to compare
tor_addr_port_t values for equality.

Bugfix on c2c5b13e5d8a77e; bug not in any released Tor. Found by
clang's scan-build.

src/test/test_bridges.c

@@ -234,7 +234,7 @@ test_bridges_get_configured_bridge_by_orports_digest(void *arg)
   ret = get_configured_bridge_by_orports_digest(digest, orports);
   tt_ptr_op(ret, OP_NE, NULL);
 
-  tt_mem_op(addrport1, OP_EQ, bridge_get_addr_port(ret), sizeof(ret));
+  tt_assert(tor_addr_port_eq(addrport1, bridge_get_addr_port(ret)));
 
  done:
   smartlist_free(orports);