Fix syscalls on different archs

pkg/mdns/syscall.go

@@ -0,0 +1,13 @@
+//go:build darwin || linux
+
+package mdns
+
+import "syscall"
+
+func SetsockoptInt(fd uintptr, level, opt int, value int) (err error) {
+	return syscall.SetsockoptInt(int(fd), level, opt, value)
+}
+
+func SetsockoptIPMreq(fd uintptr, level, opt int, mreq *syscall.IPMreq) (err error) {
+	return syscall.SetsockoptIPMreq(int(fd), level, opt, mreq)
+}