rxrpc: Ask the security class how much space to allow in a packet

Ask the security class how much header and trailer space to allow for when
allocating a packet, given how much data is remaining.

This will allow the rxgk security class to stick both a trailer in as well
as a header as appropriate in the future.

Signed-off-by: David Howells <dhowells@redhat.com>

net/rxrpc/conn_object.c

@@ -49,7 +49,6 @@ struct rxrpc_connection *rxrpc_alloc_connection(gfp_t gfp)
 		conn->security = &rxrpc_no_security;
 		spin_lock_init(&conn->state_lock);
 		conn->debug_id = atomic_inc_return(&rxrpc_debug_id);
-		conn->size_align = 4;
 		conn->idle_timestamp = jiffies;
 	}