- Pass a mask of the regions we wish to be probed to validate_mem
- Only take s->skt_sem if we need to probe resources on a socket

This prevents a deadlock reported by Adam Belay caused by ds.c waiting
with the socket semaphore held for userspace to respond.  Meanwhile,
userspace may under some rare circumstances issue a request to read
tuples from the card, which tries to take the socket semaphore again.