rxrpc: Fix the return value of rxrpc_new_incoming_call()

Dan Carpenter sayeth[1]:

  The patch 5e6ef4f1: "rxrpc: Make the I/O thread take over the
  call and local processor work" from Jan 23, 2020, leads to the
  following Smatch static checker warning:

	net/rxrpc/io_thread.c:283 rxrpc_input_packet()
	warn: bool is not less than zero.

Fix this (for now) by changing rxrpc_new_incoming_call() to return an int
with 0 or error code rather than bool.  Note that the actual return value
of rxrpc_input_packet() is currently ignored.  I have a separate patch to
clean that up.

Fixes: 5e6ef4f1

 ("rxrpc: Make the I/O thread take over the call and local processor work")
Reported-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org
Link: http://lists.infradead.org/pipermail/linux-afs/2022-December/006123.html [1]
Signed-off-by: David S. Miller <davem@davemloft.net>