[vty] Allow to set the RACH NM attributes on a per BTS basis

Be able to tune the RACH settings of the BTS via the vty interface,
by default they are initialized to -1 which means we will use the
content of the static array (BTS default) and can be changed via
the VTY interface. I have verified the setting on the nanoBTS with
wireshark and I have tested writing the config file.
diff --git a/openbsc/src/vty_interface.c b/openbsc/src/vty_interface.c
index dd35372..851a603 100644
--- a/openbsc/src/vty_interface.c
+++ b/openbsc/src/vty_interface.c
@@ -308,6 +308,13 @@
 	vty_out(vty, "  rach max transmission %u%s",
 		rach_max_trans_raw2val(bts->si_common.rach_control.max_trans),
 		VTY_NEWLINE);
+
+	if (bts->rach_b_thresh != -1)
+		vty_out(vty, "  rach nm busy threshold %u%s",
+			bts->rach_b_thresh, VTY_NEWLINE);
+	if (bts->rach_ldavg_slots != -1)
+		vty_out(vty, "  rach nm load average %u%s",
+			bts->rach_ldavg_slots, VTY_NEWLINE);
 	if (bts->si_common.rach_control.cell_bar)
 		vty_out(vty, "  cell barred 1%s", VTY_NEWLINE);
 	if (is_ipaccess_bts(bts)) {
@@ -1337,6 +1344,26 @@
 	return CMD_SUCCESS;
 }
 
+DEFUN(cfg_bts_rach_nm_b_thresh,
+      cfg_bts_rach_nm_b_thresh_cmd,
+      "rach nm busy threshold <0-255>",
+      "Set the NM Busy Threshold in DB")
+{
+	struct gsm_bts *bts = vty->index;
+	bts->rach_b_thresh = atoi(argv[0]);
+	return CMD_SUCCESS;
+}
+
+DEFUN(cfg_bts_rach_nm_ldavg,
+      cfg_bts_rach_nm_ldavg_cmd,
+      "rach nm load average <0-65535>",
+      "Set the NM Loadaver Slots value")
+{
+	struct gsm_bts *bts = vty->index;
+	bts->rach_ldavg_slots = atoi(argv[0]);
+	return CMD_SUCCESS;
+}
+
 DEFUN(cfg_bts_cell_barred, cfg_bts_cell_barred_cmd,
       "cell barred (0|1)",
       "Should this cell be barred from access?")
@@ -1771,6 +1798,8 @@
 	install_element(BTS_NODE, &cfg_bts_challoc_cmd);
 	install_element(BTS_NODE, &cfg_bts_rach_tx_integer_cmd);
 	install_element(BTS_NODE, &cfg_bts_rach_max_trans_cmd);
+	install_element(BTS_NODE, &cfg_bts_rach_nm_b_thresh_cmd);
+	install_element(BTS_NODE, &cfg_bts_rach_nm_ldavg_cmd);
 	install_element(BTS_NODE, &cfg_bts_cell_barred_cmd);
 	install_element(BTS_NODE, &cfg_bts_ms_max_power_cmd);
 	install_element(BTS_NODE, &cfg_bts_per_loc_upd_cmd);