tests: replace unix-yy.test with net-yy-unix.test

tests: replace unix-yy.test with net-yy-unix.test

Unlike the former test that was based on match_awk,
the new one uses match_diff and does more rigorous testing.

* tests/net-yy-unix.c: New file.
* tests/net-yy-unix.test: New test.
* tests/unix-yy.test: Remove.
* tests/unix-yy-accept.awk: Remove.
* tests/unix-yy-connect.awk: Remove.
* tests/.gitignore: Add net-yy-unix.
* tests/Makefile.am (check_PROGRAMS): Likewise.
(TESTS): Replace unix-yy.test with net-yy-unix.test.
(EXTRA_DIST): Remove unix-yy-accept.awk and unix-yy-connect.awk.