gfio: ensure all command opcode handlers are properly gdk thread protected

gfio: ensure all command opcode handlers are properly gdk thread protected

Since we get this callback from our handling thread, we
need to use gdk_threads_enter() and gdk_threads_leave()
to ensure proper locking.

This fixes various crashes.

Signed-off-by: Jens Axboe <axboe@kernel.dk>