Store IkeTunnelConnectionParams in Ikev2VpnProfile

IkeTunnelConnectionParams contains more information than the
existing fields inside Ikev2VpnProfile. If the Ikev2VpnProfile
is built from an IkeTunnelConnectionParams, saving it to the
existing fields of Ikev2VpnProfile may cause information lost,
such as IKE options. Thus, store the IkeTunnelConnectionParams
as a field inside Ikev2VpnProfile.

The other Ike options are mutually exclusive with
IkeTunnelConnectionParams. The information such as Preshared
key or username/password may not return expected values if a
profile is built from an IkeTunnelConnectionParams. This may
confuse API callers for using the other getters. Thus, expose
a getter to retrieve IkeTunnelConnectionParams

Bug: 184750836
Test: atest FrameworksNetTests
CTS-Coverage-Bug: 184750836
Change-Id: I61e9a9549b87951956afdcbae2518228994e4729