bankd: respond to IPA PING from client with IPA PONG

The bankd worker threads handle the RSPRO connection from the
remsim-clients outside of our usual osmo* infrastructure and hence
they don't inherit the common IPA CCM handling.  This means we need
to explicitly implement the keep-alive PONG support.

What this doesn't add is any outbound keepalive handling towards
the client.

Change-Id: I86f8ca28ece62c33ccbf45c9c65172be8a647407

src/bankd_main.c

@@ -670,7 +670,13 @@ restart_wait:
 	}
 
 	if (hh->proto == IPAC_PROTO_IPACCESS) {
-		LOGW(worker, "IPA CCM not implemented yet\n");
+		switch (hh->data[0]) {
+		case IPAC_MSGT_PING:
+			return ipa_ccm_send_pong(worker->client.fd);
+		default:
+			LOGW(worker, "IPA CCM 0x%02x not implemented yet\n", hh->data[0]);
+			break;
+		}
 		return 0;
 	}