Add ACTION_VPN_MANAGER_EVENT in ConstantsShim

Before T, there is no ACTION_VPN_MANAGER_EVENT in VpnManager,
so add ACTION_VPN_MANAGER_EVENT in ConstantsShim for passing
sc-mainline-prod build.

Bug: 225010642
Test: atest FrameworksNetTests
Change-Id: I61e6ce31bc80d1a18be020d0ae0b683c3eaf4679
(cherry picked from commit 91eda06d7968d80155d25cf5e6597cdc479a2ddc)
Merged-In: I61e6ce31bc80d1a18be020d0ae0b683c3eaf4679
1 file changed