Add APIs that allow to exclude routes from VPN

Add new methods to VpnService.Builder that allow to specify network
routes that should bypass the VPN. Implemented by using RTN_THROW
routes.

Bug: 186082280
Test: atest HostsideVpnTests
Test: atest VpnServiceBuilderTest
Change-Id: Ic3b10464a53a8b56334589acec8f27acdc180ff7