(Network) Check connect errno for successful connection

[MrHuu]

Description

On platforms not supporting getsockopt, use the return value from connect to verify successful socket connection.

Related Issues

• (3DS) Network issues #14381

Related Pull Requests

• (Network) Don't call getsockopt on 3DS platform #14389

Reviewers

@cthulhu-throwaway

[ghost]

Just checked the implementation on libogc (Wii; GameCube doesn't have networking)... It's an abomination.
It's not compliant with POSIX at all (even Microsoft's connect is more POSIX compliant than this implementation).

1. It doesn't appear to write anything to errno.
2. It returns the error constant... as a negative value.

According to this: https://github.com/devkitPro/libogc/blob/bc4b778d558915aa40676e33514c4c9ba2af66b8/libtinysmb/smb.c#L1015-L1022
The gekko (libogc) implementation should be:

   res = connect(fd, addr->ai_addr, addr->ai_addrlen);
   if (res < 0 && -res != EISCONN)
      return false;

net_connect implementation: https://github.com/devkitPro/libogc/blob/bc4b778d558915aa40676e33514c4c9ba2af66b8/libogc/network_wii.c#L850-L871

POSIX clearly states in both POSIX.1-2001 and POSIX.1-2008:

Upon successful completion, connect() shall return 0; otherwise, -1 shall be returned and errno set to indicate the error.

[MrHuu]

That's wonderful.. I've adapted the logic to reflect this.