vty: Document some previously undocumented parameters

Katerina pointed out that some nodes are not fully documented and
proposed some messages. The token/timeout messages were correct, I
have modified the other messages. I removed the full-stop from the
PING/PONG documentation as we are normally not using a full sentence.
diff --git a/openbsc/src/libmgcp/mgcp_vty.c b/openbsc/src/libmgcp/mgcp_vty.c
index 88d793f..69984ee 100644
--- a/openbsc/src/libmgcp/mgcp_vty.c
+++ b/openbsc/src/libmgcp/mgcp_vty.c
@@ -327,7 +327,8 @@
 DEFUN(cfg_mgcp_sdp_fmtp_extra,
       cfg_mgcp_sdp_fmtp_extra_cmd,
       "sdp audio fmtp-extra .NAME",
-      "Add extra fmtp for the SDP file\n")
+      "Add extra fmtp for the SDP file\n" "Audio\n" "Fmtp-extra\n"
+      "Extra Information\n")
 {
 	char *txt = argv_concat(argv, argc, 0);
 	if (!txt)
@@ -508,7 +509,8 @@
 DEFUN(cfg_trunk_sdp_fmtp_extra,
       cfg_trunk_sdp_fmtp_extra_cmd,
       "sdp audio fmtp-extra .NAME",
-      "Add extra fmtp for the SDP file\n")
+      "Add extra fmtp for the SDP file\n" "Audio\n" "Fmtp-extra\n"
+      "Extra Information\n")
 {
 	struct mgcp_trunk_config *trunk = vty->index;
 	char *txt = argv_concat(argv, argc, 0);