Main thread priority field in the exheader should be given a proper value

[neobrain]

As outlined in https://github.com/citra-emu/citra/issues/2013#issuecomment-241234154 :

Research result:
This is due to the fake exheader generated by braindump. More specifically, exheader_header.arm11_system_local_caps.priority (=main thread priority) is set as 0 by braindump(where it should be 0x30 or so). Games / apps sometimes calculate the priority of new-created thread relative to the main thread, thus make a out-of-bound priority since the main thread priority is already wrong.

Close as this is not an issue in citra.