rxrpc: Disable IRQ, not BH, to take the lock for ->attend_link

Use spin_lock_irq(), not spin_lock_bh() to take the lock when accessing the
->attend_link() to stop a delay in the I/O thread due to an interrupt being
taken in the app thread whilst that holds the lock and vice versa.

Fixes: a2ea9a90 ("rxrpc: Use irq-disabling spinlocks between app and I/O thread")
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org
Link: https://patch.msgid.link/2870146.1734037095@warthog.procyon.org.uk


Signed-off-by: Jakub Kicinski <kuba@kernel.org>