Skip sending VpnManager events for Settings VPNs

This change early-exits from the sendEventToVpnManagerApp()
method if the profile was not a VPN app.

Otherwise the sendEventToVpnManagerApp() will call
getRedactedNetworkCapabilities() which will call
AppOpsManager#checkPackage() eventually.
And AppOpsManager#checkPackage() will check if the given package
is the same as the given uid. In this case, VPN sends
"[Legacy VPN]" as the package and sends 1000 as the uid, but
there is no package named "[Legacy VPN], so the SecurityException
is thrown.

Bug: 236315805
Test: atest FrameworksNetTests:VpnTest
Change-Id: I228f62a5e09017dbf985a614f2e42434238a220c