move implementation to internal/ directory (#828)

internal/util/tcpsock/tcpsock_freebind_unsupported.go

@@ -0,0 +1,13 @@
+//go:build !linux && !freebsd
+// +build !linux,!freebsd
+
+package tcpsock
+
+import (
+	"fmt"
+	"syscall"
+)
+
+func freeBind(network, address string, c syscall.RawConn) error {
+	return fmt.Errorf("IP_FREEBIND equivalent functionality not supported  on this platform")
+}