Wait for a socket to be created before sending packets

The required sockets may not have been created yet when
MdnsServiceTypeClient#startSendAndReceive is called on
MdnsDiscoveryManager#registerListener, so the first send would go
nowhere, and only later retries would be sent. Ideally the code
would wait for some sockets to be created before calling
startSendAndReceive.

Bug: 265787401
Bug: 264634275
Test: atest FrameworksNetTests
Change-Id: Id789d564d125c0192e742d7dd246367afdb93413