Add MdnsDiscoveryManager constructor without looper

In some use cases for the MdnsDiscoveryManager, providing looper as an
argument to the MdnsDiscoveryManager constructor is not feasible. Adding
a constructor without looper can help to match those use cases. If
constructor without looper is used. The shutDown() must be called as a
part of cleanup process.

Bug: 283914408
Test: atest FrameworksNetTests
Change-Id: I0ab04d67bae127628c6d67c4b8c109201612a54b