Update definition of mdns server for macOS

This is needed to be able to use macOS's built-in DNS-SD support
bug: 111434128
Change-Id: Iedb575f1fe93bafb84a428453059977b976e8756
diff --git a/Android.bp b/Android.bp
index b5ffd42..b472344 100644
--- a/Android.bp
+++ b/Android.bp
@@ -41,6 +41,7 @@
         darwin: {
             cflags: [
                 "-DTARGET_OS_MAC",
+                "-DMDNS_UDS_SERVERPATH=\"/var/run/mDNSResponder\"",
                 "-Wno-error",
             ],
         },