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/include/osmocom/gprs/gprs_bssgp_bss.h b/include/osmocom/gprs/gprs_bssgp_bss.h
index f07ab52..ab62b66 100644
--- a/include/osmocom/gprs/gprs_bssgp_bss.h
+++ b/include/osmocom/gprs/gprs_bssgp_bss.h
@@ -57,6 +57,7 @@
 int bssgp_tx_bvc_unblock(struct bssgp_bvc_ctx *bctx);
 
 int bssgp_tx_bvc_reset(struct bssgp_bvc_ctx *bctx, uint16_t bvci, uint8_t cause);
+int bssgp_tx_bvc_reset2(struct bssgp_bvc_ctx *bctx, uint16_t bvci, uint8_t cause, bool add_cell_id);
 
 int bssgp_tx_ul_ud(struct bssgp_bvc_ctx *bctx, uint32_t tlli,
 		   const uint8_t *qos_profile, struct msgb *llc_pdu);