Honor IP protocol set by client in non-auto IP selection mode

If automatic IP version selection is not enabled and VPN clients
set the IP version and encap type in the IkeSessionParams, VPN
should use the value set by clients instead of always setting them
to auto.

Test: atest FrameworksNetTests
Change-Id: Icd76b06cb9155b0d1fc62811daeafe89d2e45149