fix SO_MARK on non-linux OS

Makefile

@@ -2,7 +2,7 @@ NAME=gost
 BINDIR=bin
 VERSION=$(shell cat gost.go | grep 'Version =' | sed 's/.*\"\(.*\)\".*/\1/g')
 GOBUILD=CGO_ENABLED=0 go build --ldflags="-s -w" -v -x -a
-GOFILES=cmd/gost/*
+GOFILES=cmd/gost/*.go
 
 PLATFORM_LIST = \
 	darwin-amd64 \

chain.go

@@ -133,10 +133,6 @@ func (c *Chain) DialContext(ctx context.Context, network, address string, opts .
 	return
 }
 
-func setSocketMark(fd int, value int) (e error) {
-	return syscall.SetsockoptInt(fd, syscall.SOL_SOCKET, syscall.SO_MARK, value)
-}
-
 func (c *Chain) dialWithOptions(ctx context.Context, network, address string, options *ChainOptions) (net.Conn, error) {
 	if options == nil {
 		options = &ChainOptions{}

sockopts_linux.go

@@ -0,0 +1,7 @@
+package gost
+
+import "syscall"
+
+func setSocketMark(fd int, value int) (e error) {
+	return syscall.SetsockoptInt(fd, syscall.SOL_SOCKET, syscall.SO_MARK, value)
+}

sockopts_other.go

@@ -0,0 +1,7 @@
+//go:build !linux
+
+package gost
+
+func setSocketMark(fd int, value int) (e error) {
+	return nil
+}