gtphub: log: limit length of hex dumps.

The debug log prints the received/sent bytes in hex. When this data surpasses
the buffer size available for the log string (4096), the log is truncated
and lacks a newline character. Limit the amount of dumped bytes to 1000.

Sponsored-by: On-Waves ehi
diff --git a/openbsc/src/gprs/gtphub_sock.c b/openbsc/src/gprs/gtphub_sock.c
index 699672e..60bebaa 100644
--- a/openbsc/src/gprs/gtphub_sock.c
+++ b/openbsc/src/gprs/gtphub_sock.c
@@ -50,8 +50,10 @@
 		LOG(LOGL_ERROR, "sent(%d) != data_len(%d)\n",
 		    (int)sent, (int)buf_len);
 	else
-		LOG(LOGL_DEBUG, "Sent %d: %s\n",
-		    (int)sent, osmo_hexdump(buf, sent));
+		LOG(LOGL_DEBUG, "Sent %d: %s%s\n",
+		    (int)sent,
+		    osmo_hexdump(buf, sent > 1000? 1000 : sent),
+		    sent > 1000 ? "..." : "");
 
 	return 0;
 }