tls: rx: fix return value for async crypto

Gaurav reports that TLS Rx is broken with async crypto
accelerators. The commit under fixes missed updating
the retval byte counting logic when updating how records
are stored. Even tho both before and after the change
'decrypted' was updated inside the main loop, it was
completely overwritten when processing the async
completions. Now that the rx_list only holds
non-zero-copy records we need to add, not overwrite.

Reported-and-bisected-by: Gaurav Jain <gaurav.jain@nxp.com>
Fixes: cbbdee9 ("tls: rx: async: don't put async zc on the list")
Link: https://bugzilla.kernel.org/show_bug.cgi?id=217064
Tested-by: Gaurav Jain <gaurav.jain@nxp.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Link: https://lore.kernel.org/r/20230227181201.1793772-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/tls/tls_sw.c

@@ -2127,7 +2127,7 @@ int tls_sw_recvmsg(struct sock *sk,
 		else
 			err = process_rx_list(ctx, msg, &control, 0,
 					      async_copy_bytes, is_peek);
-		decrypted = max(err, 0);
+		decrypted += max(err, 0);
 	}
 
 	copied += decrypted;