Add NetworkStackModuleTest exclusion for ConnectivityCoverageTests in TEST_MAPPING.

testTetherZeroLengthDhcpPacket requires to install both Tethering
and NetworkStack modules, add NetworkStackModuleTest annotation for
ConnectivityCoverageTests running as presubmit to exclude the
testTetherZeroLengthDhcpPacket from presubmit.

Bug: 287798985
Test: TH
Change-Id: I2e21e2623b181e678189ca7758210be1b5409ae7