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.
This roughly doubles our test coverage of the bridges.c module.
* ADD new testing module, .../src/test/test_bridges.c.
* CHANGE a few function declarations from `static` to `STATIC`.
* CHANGE one function in transports.c, transport_get_by_name(), to be
mockable.
* CLOSES#25425: https://bugs.torproject.org/25425