Revert "ipa_ccm_idtag_parse*: Fix reported length value"

This reverts commit 1261db15058cfa94615f26c1083bb8a38d09218b.

The patch broke openbsc's external tests, and currently it is unclear
whether it is just an error in the test or if openbsc makes wrong
assumptions about the length value. Let's revert the patch to unblock
the master-openbsc jenkins job.

Related: OS#3851
Change-Id: I9adea35ff6de36c1611c7f85dde1b15bc1c0e786
diff --git a/src/gsm/ipa.c b/src/gsm/ipa.c
index b6fdc98..d423c26 100644
--- a/src/gsm/ipa.c
+++ b/src/gsm/ipa.c
@@ -128,7 +128,7 @@
 
 		DEBUGPC(DLMI, "%s='%s' ", ipa_ccm_idtag_name(t_tag), cur);
 
-		dec->lv[t_tag].len = t_len - 1 - len_offset;
+		dec->lv[t_tag].len = t_len - len_offset;
 		dec->lv[t_tag].val = cur;
 
 		cur += t_len - len_offset;