multi-ARFCN: fix maximum number of carriers limitation

Maximum number of carriers is fixed to 3 channels on a single
physical RF channel in multi-ARFCN mode. For some reason, it
was limited to 5.

Let's fix this, and also follow this limitation in the
following VTY command handlers:

  - cfg_multi_arfcn_cmd,
  - cfg_chan_cmd.

Change-Id: I66a1462f368458afd313ee6f0bc0abc496dde817
diff --git a/CommonLibs/trx_vty.h b/CommonLibs/trx_vty.h
index 8d251ee..8e91113 100644
--- a/CommonLibs/trx_vty.h
+++ b/CommonLibs/trx_vty.h
@@ -6,7 +6,10 @@
 
 extern struct vty_app_info g_vty_info;
 
+/* Maximum number of physical RF channels */
 #define TRX_CHAN_MAX 8
+/* Maximum number of carriers in multi-ARFCN mode */
+#define TRX_MCHAN_MAX 3
 
 /* Samples-per-symbol for downlink path
  *     4 - Uses precision modulator (more computation, less distortion)