Fix build failure on illumos

Previously v2ray can not be built on illumos due to following reasons:
1. missing build tags in transport/internet/sockopt_other.go
2. many definitions in syscall does not exist on illumos
This commit addresses these problems by adding missing build tags, and
updates those missing syscall deps on illumos to use x/sys/unix.

transport/internet/domainsocket/listener.go

@@ -9,8 +9,9 @@ import (
 	gotls "crypto/tls"
 	"os"
 	"strings"
-	"syscall"
 
+	"golang.org/x/sys/unix"
+	
 	"v2ray.com/core/common"
 	"v2ray.com/core/common/net"
 	"v2ray.com/core/transport/internet"
@@ -104,7 +105,7 @@ func (fl *fileLocker) Acquire() error {
 	if err != nil {
 		return err
 	}
-	if err := syscall.Flock(int(f.Fd()), syscall.LOCK_EX); err != nil {
+	if err := unix.Flock(int(f.Fd()), unix.LOCK_EX); err != nil {
 		f.Close()
 		return newError("failed to lock file: ", fl.path).Base(err)
 	}
@@ -113,7 +114,7 @@ func (fl *fileLocker) Acquire() error {
 }
 
 func (fl *fileLocker) Release() {
-	if err := syscall.Flock(int(fl.file.Fd()), syscall.LOCK_UN); err != nil {
+	if err := unix.Flock(int(fl.file.Fd()), unix.LOCK_UN); err != nil {
 		newError("failed to unlock file: ", fl.path).Base(err).WriteToLog()
 	}
 	if err := fl.file.Close(); err != nil {