[FUI24] Use getAllNetworkStateSnapshot in NetworkPolicyManagerService

Currently, in NPMS, getAllNetworkState is used to get all
information of all connected networks. However, this will not
be available after ConnectivityService goes to mainline module.

Thus, replace the usage with new API.

Test: atest NetworkPolicyManagerServiceTest
Bug: 174123988
Change-Id: I99bca71cb3b98f74eab036fac4517ee926eb539c