getprotobyname should not be used

The function getprotobyname is not thread-safe; it returns a pointer to a statically allocated structure. It should not be used.

The function is used to retrieve protocol number for TCP. There's a compile-time constant IPPROTO_TCP that can be used instead. While the protocol number for TCP could theoretically be changed, this is something we have never observed in practice, and it probably doesn't make sense to test.