Skip adding ingress discard rule to legacy VPN

Some legacy VPNs 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:1b376f0fc40dd121cea2b4f523ab836c61ae5318)
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:9a0a647f50dde062bb0846a87961607b4ca1c4c8)
Merged-In: Iad06dc69c5bf5ccda476e89ed9b0fc1bc63d2ebe
Change-Id: Iad06dc69c5bf5ccda476e89ed9b0fc1bc63d2ebe
2 files changed