add getprotobyname and associated functions from netdb.h. Add test_getpr...

add implementations for getprotobyname and associated functions from netdb.h.

Add test_getprotobyname.c test suite and update test_sockets.py to include test_getprotobyname.

./runner.py sockets.test_getprotobyname completes successfully.

Note only tcp and udp entries have been included, it's pretty trivial to add more, but I'd guess that the benefit would be limited and probably adds unnecessary bloat.