Support AIX SO_REUSEADDR and SO_REUSEPORT (#1328)

* Update reuseport.go

* Create reuseport_aix.go

reuseport/reuseport.go

@@ -1,5 +1,5 @@
-//go:build !windows
-// +build !windows
+//go:build !windows && !aix
+// +build !windows,!aix
 
 // Package reuseport provides TCP net.Listener with SO_REUSEPORT support.
 //

reuseport/reuseport_aix.go

@@ -0,0 +1,25 @@
+package reuseport
+
+import (
+	"context"
+	"net"
+	"syscall"
+
+	"golang.org/x/sys/unix"
+)
+
+var listenConfig = net.ListenConfig{
+	Control: func(network, address string, c syscall.RawConn) (err error) {
+		return c.Control(func(fd uintptr) {
+			err = unix.SetsockoptInt(int(fd), unix.SOL_SOCKET, unix.SO_REUSEADDR, 1)
+			if err == nil {
+				err = unix.SetsockoptInt(int(fd), unix.SOL_SOCKET, unix.SO_REUSEPORT, 1)
+			}
+		})
+	},
+}
+
+// Listen returns TCP listener with SO_REUSEADDR and SO_REUSEPORT option set, so it uses
+func Listen(network, addr string) (net.Listener, error) {
+	return listenConfig.Listen(context.Background(), network, addr)
+}