mobilebackup: add internal mobilebackup_receive_message() for cleaner code
mobilebackup: add internal mobilebackup_receive_message() for cleaner code

This does not clean up too much for now, but when completing the rest of
the mobilebackup API it will help to provide nice and clean code.

libimobiledevice-win32/libimobiledevice,kalev/libimobiledevice,Tatsh/libimobiledevice,libimobiledevice/libimobiledevice,patweb/libimobiledevice,patweb/libimobiledevice,patweb/libimobiledevice,kalev/libimobiledevice,libimobiledevice-win32/libimobiledevice,Tatsh/libimobiledevice,upbit/libimobiledevice,libimobiledevice-win32/libimobiledevice,kalev/libimobiledevice,libimobiledevice/libimobiledevice,Tatsh/libimobiledevice,Tatsh/libimobiledevice,upbit/libimobiledevice,libimobiledevice-win32/libimobiledevice,upbit/libimobiledevice