mDNSResponder: Update to v765.1.2

The sources can be obtained via:

https://opensource.apple.com/tarballs/mDNSResponder/mDNSResponder-765.1.2.tar.gz

Move mDNS_StartResolveService() and mDNS_StopResolveService() to an
RTEMS-specific file (rtemsbsd/mdns/mDNSResolveService.c) using the
v576.30.4 implementation.  Apple removed these functions without
explanation.

Update #3522.

mDNSResponder/unittests/InterfaceTest.h

@@ -0,0 +1,9 @@
+
+#ifndef InterfaceTest_h
+#define InterfaceTest_h
+
+#include "unittest.h"
+
+int InterfaceTest(void);
+
+#endif /* InterfaceTest_h */