rxrpc: Drop channel number field from rxrpc_call struct

Drop the channel number (channel) field from the rxrpc_call struct to
reduce the size of the call struct.  The field is redundant: if the call is
attached to a connection, the channel can be obtained from there by AND'ing
with RXRPC_CHANNELMASK.

Signed-off-by: David Howells <dhowells@redhat.com>
diff --git a/net/rxrpc/rxkad.c b/net/rxrpc/rxkad.c
index 63afa9e9..89f475f 100644
--- a/net/rxrpc/rxkad.c
+++ b/net/rxrpc/rxkad.c
@@ -275,7 +275,7 @@
 	memcpy(&iv, call->conn->csum_iv.x, sizeof(iv));
 
 	/* calculate the security checksum */
-	x = call->channel << (32 - RXRPC_CIDSHIFT);
+	x = (call->cid & RXRPC_CHANNELMASK) << (32 - RXRPC_CIDSHIFT);
 	x |= sp->hdr.seq & 0x3fffffff;
 	call->crypto_buf[0] = htonl(sp->hdr.callNumber);
 	call->crypto_buf[1] = htonl(x);
@@ -507,7 +507,7 @@
 	memcpy(&iv, call->conn->csum_iv.x, sizeof(iv));
 
 	/* validate the security checksum */
-	x = call->channel << (32 - RXRPC_CIDSHIFT);
+	x = (call->cid & RXRPC_CHANNELMASK) << (32 - RXRPC_CIDSHIFT);
 	x |= sp->hdr.seq & 0x3fffffff;
 	call->crypto_buf[0] = htonl(call->call_id);
 	call->crypto_buf[1] = htonl(x);