improve documentation of templates used in GGSN_Tests

Various improvements to the comments documenting packet templates
used in GGSN_Tests: fix IPv4 vs. IPv6 confusion, clearly indicate
whether templates are used for sending or for receiving/matching
packets, and add a missing comment.

Found while studying code to prepare for issue OS#2519.

Change-Id: I3bfc21a5ba74e0505457e4874f93501ad7c68b7b
Related: OS#2519
diff --git a/ggsn_tests/GGSN_Tests.ttcn b/ggsn_tests/GGSN_Tests.ttcn
index f320c20..2b7de96 100644
--- a/ggsn_tests/GGSN_Tests.ttcn
+++ b/ggsn_tests/GGSN_Tests.ttcn
@@ -227,7 +227,7 @@
 	/* IPv6 neighbor solicitation fe80::2 -> ff02::1:ff00:2 from 02:88:b5:1f:25:59 */
 	const octetstring c_neigh_solicit:= '6000000000203afffe800000000000000000000000000002ff0200000000000000000001ff00000287009f9600000000fe80000000000000000000000000000201010288b51f2559'O;
 
-	/* template for an ICMPv6 echo request */
+	/* template for sending an ICMPv4 echo request */
 	template PDU_ICMP ts_ICMPv4_ERQ := {
 		echo := {
 			type_field := 8,
@@ -239,7 +239,7 @@
 		}
 	}
 
-	/* template for an ICMPv6 echo request */
+	/* template for receiving/matching an ICMPv4 echo request */
 	template PDU_ICMP tr_ICMPv4_ERQ := {
 		echo := {
 			type_field := 8,
@@ -251,7 +251,7 @@
 		}
 	}
 
-	/* template for an ICMPv4 echo reply */
+	/* template for receiving/matching an ICMPv4 echo reply */
 	template PDU_ICMP tr_ICMPv4_ERP(template octetstring data := *) := {
 		echo_reply := {
 			type_field := 0,
@@ -312,7 +312,7 @@
 		}
 	}
 
-	/* template for an ICMPv6 echo request */
+	/* template for sending an ICMPv6 echo request */
 	template PDU_ICMPv6 ts_ICMPv6_ERQ := {
 		echoRequest := {
 			typeField := 128,
@@ -324,7 +324,7 @@
 		}
 	}
 
-	/* template for an ICMPv6 router solicitation */
+	/* template for sending an ICMPv6 router solicitation */
 	template PDU_ICMPv6 ts_ICMPv6_RS := {
 		routerSolicitation := {
 			typeField := 133,
@@ -336,7 +336,7 @@
 		}
 	}
 
-	/* template for an ICMPv6 router advertisement */
+	/* template for sending an ICMPv6 router advertisement */
 	template PDU_ICMPv6 ts_ICMPv6_RA(OCT16 prefix, INT1 prefix_len) := {
 		routerAdvertisement := {
 			typeField := 134,
@@ -355,6 +355,7 @@
 		}
 	}
 
+	/* template for sending an ICMPv6 neighbor solicitation */
 	template PDU_ICMPv6 ts_ICMPv6_NS(OCT16 target_addr) := {
 		neighborSolicitation := {
 			typeField := 135,
@@ -414,7 +415,7 @@
 		}
 	}
 
-	/* template for an ICMPv6 echo request */
+	/* template for receiving/matching an ICMPv6 echo request */
 	template PDU_ICMPv6 tr_ICMPv6_ERQ := {
 		echoRequest := {
 			typeField := 128,