Allow VPN network agent to exclude local traffic

Add API to allow network agent to set whether the local traffic
is excluded from the network. This commit is nonfunctional
currently but only storing the boolean inside the NAI.

Bug: 184750836
Test: atest FrameworksNetTests
Change-Id: I3799216ac8fdf22eb4bcabc6c6136d8edbf69360
3 files changed