Move extended PDP logging macro to header

It might be useful for any user of libgtp who uses libosmocore so let's
make generalized version of it available as part of installable header.

Change-Id: I79aba10ef989384a28f059c30899e65c771ae5e1
Related: SYS#3610

TODO-RELEASE

@@ -8,3 +8,4 @@
 # If any interfaces have been removed or changed since the last public release: c:r:0.
 #library	what		description / commit summary line
 libgtp		pdp.h		Addition of new tx_gpdu_seq struct member member
+libgtp		pdp.h		add LOGPDPX() helper to public API

ggsn/ggsn.c

@@ -83,8 +83,7 @@ struct ul255_t apn;
 #define LOGPGGSN(level, ggsn, fmt, args...)			\
 	LOGP(DGGSN, level, "GGSN(%s): " fmt, (ggsn)->cfg.name, ## args)
 
-#define LOGPPDP(level, pdp, fmt, args...)			\
-	LOGP(DGGSN, level, "PDP(%s:%u): " fmt, imsi_gtp2str(&(pdp)->imsi), (pdp)->nsapi, ## args)
+#define LOGPPDP(level, pdp, fmt, args...) LOGPDPX(DGGSN, level, pdp, fmt, ## args)
 
 static int ggsn_tun_fd_cb(struct osmo_fd *fd, unsigned int what);
 static int cb_tun_ind(struct tun_t *tun, void *pack, unsigned len);

gtp/pdp.h

@@ -17,6 +17,9 @@
 
 struct gsn_t;
 
+#define LOGPDPX(ss, level, pdp, fmt, args...)				\
+	LOGP(ss, level, "PDP(%s:%u): " fmt, imsi_gtp2str(&(pdp)->imsi), (pdp)->nsapi, ## args)
+
 #define PDP_MAX 1024		/* Max number of PDP contexts */
 #define PDP_MAXNSAPI 16		/* Max number of NSAPI */