pfcp ie: tweak CP Function Features

The spec indicates three bytes of CP Function Features, but both
wireshark and ttcn3 expect only one byte. This makes sense because only
eight CP F.F. flags are defined.

Drop those two always-zero bytes, hence pass the wireshark dissector and
ttcn3 parsing without warnings.

Related: SYS#5599
Change-Id: Icda891a2f3401e58f142f229465403d5dc8befe5

include/osmocom/pfcp/pfcp_ies_custom.h

@@ -73,7 +73,7 @@ struct osmo_pfcp_ie_up_function_features {
  *     printf("%s\n", osmo_pfcp_bits_to_str_c(x.bits, osmo_pfcp_cp_feature_strs));
  */
 struct osmo_pfcp_ie_cp_function_features {
-	uint8_t bits[3];
+	uint8_t bits[1];
 };
 
 /* 3GPP TS 29.244 8.2.37 */