sms/dtap: Add log messages to analyse SMS message loss

Incoming DTAP messages from MS are discarded during silent calls,
which leads to the repeated delivery of SMS since the ACKs are not
being processed.

This patch adds some log messages that have been helpful to track
this down.

Sponsored-by: On-Waves ehf
diff --git a/openbsc/src/libmsc/gsm_04_08.c b/openbsc/src/libmsc/gsm_04_08.c
index bc4a9c3..cd2a0b5 100644
--- a/openbsc/src/libmsc/gsm_04_08.c
+++ b/openbsc/src/libmsc/gsm_04_08.c
@@ -3303,6 +3303,7 @@
 	uint8_t pdisc = gh->proto_discr & 0x0f;
 	int rc = 0;
 
+	LOGP(DRLL, LOGL_DEBUG, "Dispatching 04.08 message, pdisc=%d\n", pdisc);
 	if (silent_call_reroute(conn, msg))
 		return silent_call_rx(conn, msg);