Add a new counter "rsl:ipa_nack" to count number of IPA related NACKs

Those NACKs (CRCX/MDCX/PDCH_ACT) shouldn't happen in production, and
if they do, you probably want to have a more persistent figure than
a line in the log file about it.  Having counters allows the user
to monitor this efficiently.

Change-Id: I5edf979c9a2b4c9a5a60eef9f66c26da54f2bddf
diff --git a/include/osmocom/bsc/gsm_data.h b/include/osmocom/bsc/gsm_data.h
index 0341138..7cd7539 100644
--- a/include/osmocom/bsc/gsm_data.h
+++ b/include/osmocom/bsc/gsm_data.h
@@ -204,6 +204,7 @@
 	BTS_CTR_CHAN_ACT_TOTAL,
 	BTS_CTR_CHAN_ACT_NACK,
 	BTS_CTR_RSL_UNKNOWN,
+	BTS_CTR_RSL_IPA_NACK,
 };
 
 static const struct rate_ctr_desc bts_ctr_description[] = {
@@ -226,6 +227,7 @@
 	[BTS_CTR_CHAN_ACT_TOTAL] =		{"chan_act:total", "Total number of Channel Activations."},
 	[BTS_CTR_CHAN_ACT_NACK] =		{"chan_act:nack", "Number of Channel Activations that the BTS NACKed"},
 	[BTS_CTR_RSL_UNKNOWN] =			{"rsl:unknown", "Number of unknown/unsupported RSL messages received from BTS"},
+	[BTS_CTR_RSL_IPA_NACK] =		{"rsl:ipa_nack", "Number of IPA (RTP/dyn-PDCH) related NACKs received from BTS"},
 };
 
 static const struct rate_ctr_group_desc bts_ctrg_desc = {