vty: fix documentation for 'ext-rach (disable|enable)'

Do not use 'extended' because it's not the same 11-bit Access Burst,
as it was assumed before.  Add missing docs for 'enable'/'disable'.

Change-Id: I80b5a584e554eb7cc2416017b10fee032202b372
diff --git a/CommonLibs/trx_vty.c b/CommonLibs/trx_vty.c
index eeabcbe..e672928 100644
--- a/CommonLibs/trx_vty.c
+++ b/CommonLibs/trx_vty.c
@@ -298,7 +298,9 @@
 
 DEFUN(cfg_ext_rach, cfg_ext_rach_cmd,
 	"ext-rach (disable|enable)",
-	"Enable extended (11-bit) RACH (default=disable)\n")
+	"11-bit Access Burst correlation support (default=disable)\n"
+	"Disable 11-bit Access Burst (TS1 & TS2) correlation\n"
+	"Enable 11-bit Access Burst (TS1 & TS2) correlation\n")
 {
 	struct trx_ctx *trx = trx_from_vty(vty);