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
diff --git a/ggsn/ggsn.c b/ggsn/ggsn.c
index 780a0c2..462b395 100644
--- a/ggsn/ggsn.c
+++ b/ggsn/ggsn.c
@@ -83,8 +83,7 @@
 #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);