Allow Common flags 0x94 and ignore them in PDP activation

extended from https://github.com/osmocom/openggsn/pull/2

Change-Id: I31b3e4b378e74bb5a0a2f54af6d2a15b629876cf
diff --git a/gtp/gtpie.c b/gtp/gtpie.c
index 6ffa184..68422f0 100644
--- a/gtp/gtpie.c
+++ b/gtp/gtpie.c
@@ -491,6 +491,7 @@
 		case GTPIE_TRIGGER_ID:
 		case GTPIE_OMC_ID:
 		case GTPIE_CHARGING_ADDR:
+		case GTPIE_COMMON_FLAGS:
 		case GTPIE_RAT_TYPE:
 		case GTPIE_USER_LOC:
 		case GTPIE_MS_TZ:
@@ -616,6 +617,7 @@
 			case GTPIE_TRIGGER_ID:
 			case GTPIE_OMC_ID:
 			case GTPIE_CHARGING_ADDR:
+			case GTPIE_COMMON_FLAGS:
 			case GTPIE_PRIVATE:
 				iesize = 3 + hton16(ie[i]->tlv.l);
 				break;
@@ -722,6 +724,7 @@
 				case GTPIE_TRIGGER_ID:
 				case GTPIE_OMC_ID:
 				case GTPIE_CHARGING_ADDR:
+				case GTPIE_COMMON_FLAGS:
 				case GTPIE_PRIVATE:
 					iesize = 3 + hton16(ie[i].tlv.l);
 					break;
diff --git a/gtp/gtpie.h b/gtp/gtpie.h
index 754382e..8ea19ea 100644
--- a/gtp/gtpie.h
+++ b/gtp/gtpie.h
@@ -104,6 +104,7 @@
 #define GTPIE_EXT_HEADER_T  141	/* Extension Header Type List */
 #define GTPIE_TRIGGER_ID    142	/* Trigger Id */
 #define GTPIE_OMC_ID        143	/* OMC Identity */
+#define GTPIE_COMMON_FLAGS  148	/* Common Flags */
 #define GTPIE_RAT_TYPE      151	/* Radio Access Technology Type */
 #define GTPIE_USER_LOC      152	/* User Location Information  */
 #define GTPIE_MS_TZ         153	/* MS Time Zone */