gprs: Add LOGGSUBSCRP macro to log subscriber info

This patch adds a new logging macro, that logs to DGPRS and provides
a uniform prefix containing the IMSI without using the mm reference.
This is an improvement over using LOGMMCTXP, since the new macro also
provides an IMSI if no MM context is attached.

Sponsored-by: On-Waves ehf

openbsc/include/openbsc/gprs_sgsn.h

@@ -278,6 +278,10 @@ struct sgsn_subscriber_data {
 	int			error_cause;
 };
 
+#define LOGGSUBSCRP(level, subscr, fmt, args...) \
+	LOGP(DGPRS, level, "SUBSCR(%s) " fmt, (subscr)->imsi, \
+	     ## args)
+
 struct sgsn_config;
 struct sgsn_instance;
 extern const struct value_string *sgsn_auth_state_names;