[CTT-5] Stop update TCP conntrack entry timeout

This is a preparation for only update the tcp timeout while
adding rules. Also add slack time for updating UDP timeout
interval.

Bug: 190783768
Bug: 192804833

Test: atest TetheringCoverageTests
Change-Id: I3151b531e6581e257f3cfa39ad2fcf1650358b3d
2 files changed