This commit optimizes the mechanism to examine the TCP sockets
based on the VPN UID range.

The automaticOnOffKeepalives will be paused/resumed by checking
the TCP sockets status on the VPN network. The existing design
considers all UIDs, not the UID ranges for the specific VPN
network. This may lead to an inaccurate judgement to not to
stop the keepalive even when there is no socket on the VPN
network.

This commit is also a part of follow-up work from aosp/2354202
to use structized class to parse the TCP sockets.

Bug: 311119352
Bug: 265877161
Test: atest FrameworksNetTests
Change-Id: I4a6b751cb904b9c18ed1df420cc880ea38022d6a