rxrpc: Create a null security type and get rid of conditional calls

Create a null security type for security index 0 and get rid of all
conditional calls to the security operations.  We expect normally to be
using security, so this should be of little negative impact.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/rxrpc/ar-ack.c b/net/rxrpc/ar-ack.c
index 3cd9264..374478e 100644
--- a/net/rxrpc/ar-ack.c
+++ b/net/rxrpc/ar-ack.c
@@ -588,7 +588,8 @@
 		_proto("OOSQ DATA %%%u { #%u }", sp->hdr.serial, sp->hdr.seq);
 
 		/* secured packets must be verified and possibly decrypted */
-		if (rxrpc_verify_packet(call, skb, _abort_code) < 0)
+		if (call->conn->security->verify_packet(call, skb,
+							_abort_code) < 0)
 			goto protocol_error;
 
 		rxrpc_insert_oos_packet(call, skb);