add DLCX command statistics to osmo-mgw

Add a counter group for DLCX commands. The group contains counters for
successful connection processing as well as various error conditions.
This provides a quick overview of DLCX failures on each trunk throughout
the lifetime of the osmo-mgw process.

The counters are displayed by 'show mgcp stats' and 'show rate-counters'

While here, rename MGCP_MDCX_FAIL_DEFERRED_BY_POLICY to
MGCP_MDCX_DEFERRED_BY_POLICY; we have decided that deferred connections
aren't failures, and this keeps names used by DLCX and MDCX in sync.

Also remove some allocation failure checks with OSMO_ASSERT(); such
checks aren't en vogue anymore.

Change-Id: Ie0dde2faf02fd68a69f986973d39b1bea367039b
Depends: I80d36181600901ae2e0f321dc02b5d54ddc94139I
Related: OS#2660
diff --git a/src/libosmo-mgcp/mgcp_vty.c b/src/libosmo-mgcp/mgcp_vty.c
index e40d412..83f845a 100644
--- a/src/libosmo-mgcp/mgcp_vty.c
+++ b/src/libosmo-mgcp/mgcp_vty.c
@@ -249,6 +249,10 @@
 		vty_out(vty, "   %s:%s", cfg->mgcp_crcx_ctr_group->desc->group_description, VTY_NEWLINE);
 		vty_out_rate_ctr_group_fmt(vty, "   %25n: %10c (%S/s %M/m %H/h %D/d) %d", cfg->mgcp_crcx_ctr_group);
 	}
+	if (show_stats && cfg->mgcp_dlcx_ctr_group) {
+		vty_out(vty, "   %s:%s", cfg->mgcp_dlcx_ctr_group->desc->group_description, VTY_NEWLINE);
+		vty_out_rate_ctr_group_fmt(vty, "   %25n: %10c (%S/s %M/m %H/h %D/d) %d", cfg->mgcp_dlcx_ctr_group);
+	}
 	if (show_stats && cfg->mgcp_mdcx_ctr_group) {
 		vty_out(vty, "   %s:%s", cfg->mgcp_mdcx_ctr_group->desc->group_description, VTY_NEWLINE);
 		vty_out_rate_ctr_group_fmt(vty, "   %25n: %10c (%S/s %M/m %H/h %D/d) %d", cfg->mgcp_mdcx_ctr_group);