Add MdnsReplySenderTest

Currently, the MdnsReplySender doesn't have a dedicated test
class to verify its functionality. To address this gap, add the
MdnsReplySenderTest class, which can test all methods within the
MdnsReplySender class.

Bug: 312657709
Test: atest FrameworksNetTests
Change-Id: Ibd948d97d38c012c63092ed4c6877d04b1ff14c1