Under rare but benign circumstances (on XNU), incoming datagrams appear
to be dropped by the operating system after libuv has been notified of
their arrival but before libuv has had a chance to receive them.
Fixes: https://github.com/libuv/libuv/issues/4219
Switch from old-style ASSERT macro to new-style ASSERT_EQ,... macros.
Using new-style macros makes it easier to debug test failures
Fixes: https://github.com/libuv/libuv/issues/2974
Pass the loop to MAKE_VALGRIND_HAPPY() so it's explicit on which loop
needs to be cleaned up. Since it asserts on uv_loop_close(), need to
remove a couple of those that were being done before the call.
Cleanup where loop was assigned, so the entire test either uses loop or
uv_default_loop(). Not both.
Also take care of any reqs that may have been left uncleaned.
