Fix gdb ports not closing after restarting/crashing

[GalaxyShard]

In some cases restarting melonDS with GDB enabled will produce the following error:

[GDB] err: can't bind to address <any> and port 7000

This PR should fix the error by enabling SO_REUSEADDR on the socket opened for the GDB stub. With this patch I can no longer reproduce the above error.