Replace strncpy() with inet_ntop() to prevent potential truncation
Cast tcplen to size_t to resolve signedness comparison warning.

Changes:
- Use ``inet_ntop(AF_INET, &bullshit, sourcehost, sizeof(sourcehost))``
  instead of ``strncpy(sourcehost, inet_ntoa(bullshit), 16)`` to ensure
string termination
- Cast tcplen to size_t in assert
```c
assert((size_t)tcplen >= sizeof(tcp))
```
to remove the -Wsign-compare warning

This removes compiler warnings and improves code safety.