Add: Through load speed limit setting

src/saveload/afterload.cpp

@@ -3995,6 +3995,10 @@ bool AfterLoadGame()
 		_settings_game.station.station_delivery_mode = SD_NEAREST_FIRST;
 	}
 
+	if (SlXvIsFeatureMissing(XSLFI_TL_SPEED_LIMIT)) {
+		_settings_game.vehicle.through_load_speed_limit = 15;
+	}
+
 	InitializeRoadGUI();
 
 	/* This needs to be done after conversion. */

src/saveload/extended_ver_sl.cpp

@@ -163,6 +163,7 @@ const SlxiSubChunkInfo _sl_xv_sub_chunk_infos[] = {
 	{ XSLFI_LINKGRAPH_AIRCRAFT,     XSCF_NULL,                1,   1, "linkgraph_aircraft",        nullptr, nullptr, nullptr        },
 	{ XSLFI_COMPANY_PW,             XSCF_IGNORABLE_ALL,       1,   1, "company_password",          nullptr, nullptr, "PLYP"         },
 	{ XSLFI_ST_INDUSTRY_CARGO_MODE, XSCF_IGNORABLE_UNKNOWN,   1,   1, "st_industry_cargo_mode",    nullptr, nullptr, nullptr        },
+	{ XSLFI_TL_SPEED_LIMIT,         XSCF_IGNORABLE_UNKNOWN,   1,   1, "tl_speed_limit",            nullptr, nullptr, nullptr        },
 	{ XSLFI_SCRIPT_INT64,           XSCF_NULL,                1,   1, "script_int64",              nullptr, nullptr, nullptr        },
 	{ XSLFI_NULL, XSCF_NULL, 0, 0, nullptr, nullptr, nullptr, nullptr },// This is the end marker
 };

src/saveload/extended_ver_sl.h

@@ -117,6 +117,7 @@ enum SlXvFeatureIndex {
 	XSLFI_LINKGRAPH_AIRCRAFT,                     ///< Link graph last aircraft update field and aircraft link scaling setting
 	XSLFI_COMPANY_PW,                             ///< Company passwords
 	XSLFI_ST_INDUSTRY_CARGO_MODE,                 ///< Station industry cargo mode setting
+	XSLFI_TL_SPEED_LIMIT,                         ///< Through load maximum speed setting
 
 	XSLFI_SCRIPT_INT64,                           ///< See: SLV_SCRIPT_INT64