Skip adding ingress discard rule to OEM VPN

OEM VPNs might need to receive packets to VPN address via
non-VPN interface.

Bug: 352424251
Test: CsIngressDiscardRuleTest
(cherry picked from https://android-review.googlesource.com/q/commit:c14288f7c77a2da7de0c7af107b9b505081f465d)
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:f0fa3a4554393018b0fcab937ff0013a1829a69b)
Merged-In: Ia9000bcbb5b3b9e1e0d396ba78946be36e2fc5ba
Change-Id: Ia9000bcbb5b3b9e1e0d396ba78946be36e2fc5ba
2 files changed