Add helper method to enfore a package name belongs to an uid

This is no-op refactor to move utility methods from
ConnectivityService to a common place.

Test: atest NetworkStaticLibTests#com.android.net.moduletests.util.PermissionUtilsTest#testEnforcePackageNameMatchesUid
Bug: N/A
Change-Id: I5802dedcc91fa6e130a5c534bba5080ca37dbeec