Fix cannot create Nat-T keepalive on mobile data

Currently phone process fail to unparcel NattKeepalivePacketData
since it is not in framework. Moves NattKeepalivePacketData to
framework to make it can be utilized by telephony.

This change also removes the error feedback triggered by calling
add keepalive packet filter to an unsupported network agent. This
is misinterpreted by KeepaliveTracker that start keepalive is
failing.

Bug: 134048171
Test: 1. atest android.net.cts.ConnectivityManagerTest#testSocketKeepaliveLimitTelephony
      2. atest android.net.cts.ConnectivityManagerTest
      3. atest FrameworksNetTests
      4. atest FrameworksTelephonyTests
Change-Id: If630d5b339aa722717258c721daa8ead8c431e2d