Fix (a kind of) violation of strict aliasing rule.

Due to the rule, "sin" and "sin6" can be treated as restrict pointers.
Compilers seem to be confused by structure copy for those pointed by
them before assignments.

For aarch64eb, GCC 9 and 10 compile t_tcp.c rev 1.11 into a code, where
fetch for "sin6->sin6_port" is preceding the structure copy "ss = bs".
This results in failure of connect(2) with EADDRNOOTAVAIL.

(rin)