Set legacy type for VPN

VPN legacy type was lost when NetworkInfo was replaced by
NetworkAgentConfig.
Set legacy type when creating NetworkAgentConfig to fix it.

Original NetworkInfo log:
NI = [type: [], state: CONNECTED/CONNECTED, reason: (unspecified), extra: , failover: false, available: true, roaming: false], Type = -1
Current NetworkInfo log:
NI = [type: VPN[], state: CONNECTED/CONNECTED, reason: (unspecified), extra: , failover: false, available: true, roaming: false], Type = 17

Bug: 184261389
Test: atest CtsHostsideNetworkTests:HostsideVpnTests#testDefault
Change-Id: I237f7ff4d6899530c4ad057a84d3b8b34513be79