Use VCN policy API in Telephony.

This CL updates the use of VCN Network policies in DataConnection to use
the new API naming. The API previously defined
VcnUnderlyingNetworkPolicyListener and
VcnManager#getVcnUnderlyingNetworkPolicy. Following API Guidance, these
were renamed to VcnNetworkPolicyListener and
VcnManager#applyVcnNetworkPolicy, respectively.

Bug: 177020190
Test: atest DataConnectionTest
Change-Id: Iab05b7a7ddb170d8e3afa6290ad1e7144ec4887d