Allow kernel services using AF_RXRPC to indicate that a call should be
non-interruptible. This allows kafs to make things like lock-extension and
writeback data storage calls non-interruptible.
If this is set, signals will be ignored for operations on that call where
possible - such as waiting to get a call channel on an rxrpc connection.
It doesn't prevent UDP sendmsg from being interrupted, but that will be
handled by packet retransmission.
rxrpc_kernel_recv_data() isn't affected by this since that never waits,
preferring instead to return -EAGAIN and leave the waiting to the caller.
Userspace initiated calls can't be set to be uninterruptible at this time.
Signed-off-by: David Howells <dhowells@redhat.com>
