[AF_RXRPC]: Make it possible to merely try to cancel timers from a module

Export try_to_del_timer_sync() for use by the AF_RXRPC module.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --cc kernel/timer.c
Simple merge