Reject overlapped ranges in Network::addUsers()

Add a helper function to check if ranges are overlapped with itself or
overlapped with the existing ranges.

Bug: 176507580
Test: atest netd_integration_test
Test: atest HostsideVpnTests
Change-Id: I40ee5c4186c4697ae657bea3b63b73d5879d8d90
5 files changed