gprs_bssgp: Add bssgp_tx_bvc_reset2()

If a BVC-RESET is sent from SGSN, there must not be a cell ID IE
included.  See "Note 1" of TS 48.018 Section 10.4.12.

Change-Id: I11d4e70d510265b9c09dffccdab10b3f0816715a
diff --git a/TODO-RELEASE b/TODO-RELEASE
index 8aa2367..e2fd830 100644
--- a/TODO-RELEASE
+++ b/TODO-RELEASE
@@ -14,3 +14,4 @@
 gb		API/ABI change		deprecate gprs_nsvc_crate(); export gprs_nsvc_create2()
 gsm		API/ABI change		add new member to lapd_datalink
 gsm		new API			new gsm0808_create_common_id()
+gb		new API			new bssgp_tx_bvc_reset2()