rxrpc: Move call state changes from recvmsg to I/O thread

Move the call state changes that are made in rxrpc_recvmsg() to the I/O
thread.  This means that, thenceforth, only the I/O thread does this and
the call state lock can be removed.

This requires the Rx phase to be ended when the last packet is received,
not when it is processed.

Since this now changes the rxrpc call state to SUCCEEDED before we've
consumed all the data from it, rxrpc_kernel_check_life() mustn't say the
call is dead until the recvmsg queue is empty (unless the call has failed).

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org