use SO_REUSEPORT_LB on FreeBSD (#106)

* feat: Add support for SO_REUSEPORT_LB option as per freeBSD

* fix: address review comments

* chore: updated to use build flags

* chore: remove unnecessary code

* chore: fix gofmt error

control_freebsd.go

@@ -0,0 +1,27 @@
+//go:build freebsd
+
+package reuseport
+
+import (
+	"syscall"
+
+	"golang.org/x/sys/unix"
+)
+
+func Control(network, address string, c syscall.RawConn) (err error) {
+	controlErr := c.Control(func(fd uintptr) {
+		err = unix.SetsockoptInt(int(fd), unix.SOL_SOCKET, unix.SO_REUSEADDR, 1)
+		if err != nil {
+			return
+		}
+		err = unix.SetsockoptInt(int(fd), unix.SOL_SOCKET, unix.SO_REUSEPORT, 1)
+		if err != nil {
+			return
+		}
+		err = unix.SetsockoptInt(int(fd), unix.SOL_SOCKET, unix.SO_REUSEPORT_LB, 1)
+	})
+	if controlErr != nil {
+		err = controlErr
+	}
+	return
+}

control_unix.go

@@ -1,4 +1,4 @@
-//go:build !plan9 && !windows && !wasm
+//go:build !plan9 && !windows && !wasm && !freebsd
 
 package reuseport