LibCore: Fix SocketAddress.h compilation errors on Windows

[stasoid]

Including winsock2.h in a header file is undesirable for architectural reasons, so I pulled the needed types from ws2def.h and ws2ipdef.h into a separate header.

Files inaddr.h and afunix.h are tiny and can be included directly. They each define a single struct (in_addr and sockaddr_un respectively).

I removed the #if (_WIN32_WINNT < 0x0600) code because it is not relevant for us. It is intended for Windows XP/Windows Server 2003 and earlier, but Ladybird doesn't support 32-bit, and 64-bit Windows XP is very rare.