Require MOBIKE for IkeSessionParams in VCN configs.

This CL updates VcnGatewayConnectionConfigs to require
IkeTunnelConnectionParams with MOBIKE enabled for the
IkeSessionParams. This is necessary for VCNs - without it,
they do not support IPsec mobility (one of the main features
of the VCN).

Bug: 187851560
Test: atest FrameworksVcnTests CtsVcnTestCases
Change-Id: I94db52a8c42d9fa4681fefb8f787f006933caa18