LOCKDOWN_VPN was in the FirewallChain IntDef but this was not a right
place because LOCKDOWN_VPN was not a valid value for Connectivity APIs
that take an argument annotated with @FirewallChain(setUidFirewallRule,
setFirewallChainEnabled, replaceFirewallChain).
LOCKDOWN_VPN was in the FirewallChain IntDef because
BpfNetMaps#setUidRule was used to add/remove LOCKDOWN_VPN entries.
This commit adds BpfNetMaps#updateUidLockdownRule and uses this to
add/remove LOCKDOWN_VPN entries instead of BpfNetMaps#setUidRule and
removes LOCKDOWN from FirewallChain.
Bug: 206482423
Test: atest TrafficControllerTest ConnectivityServiceTest
PermissionMonitorTest HostsideVpnTests#testBlockIncomingPacket
Change-Id: Iff9b9792fc0f208f153e10e396c6d5034b412d7c
8b42e6d431