Implement bidirectional mode for signals on bridges/tunnels

src/table/settings.ini

@@ -3151,6 +3151,14 @@ strhelp  = STR_CONFIG_SETTING_GRAPH_LINE_THICKNESS_HELPTEXT
 strval   = STR_JUST_COMMA
 proc     = RedrawScreen
 
+[SDTC_BOOL]
+var      = gui.adv_sig_bridge_tun_modes
+flags    = SLF_NOT_IN_SAVE | SLF_NO_NETWORK_SYNC
+def      = false
+str      = STR_CONFIG_SETTING_ADV_SIG_BRIDGE_TUN_MODES
+strhelp  = STR_CONFIG_SETTING_ADV_SIG_BRIDGE_TUN_MODES_HELPTEXT
+cat      = SC_EXPERT
+
 ; For the dedicated build we'll enable dates in logs by default.
 [SDTC_BOOL]
 ifdef    = DEDICATED