Copy isBypassable flag from VpnProfile to VpnConfig

Copy isBypassable flag from VpnProfile to VpnConfig so that
ConnectivityService can set the correct config to netd when
network is created.

VpnConfig#allowBypass isn't set for platform VPN when
startVpnProfilePrivileged tries to convert the VpnProfile
to VpnConfig.

Bug: 242931436
Test: atest FrameworksNetTests:VpnTest
Change-Id: Ib0fa580bb41dcf67e23b00b79de8e0535e5c15a2