This commit adds tests that reflect outgoing packets, flipping the outer
src/dst headers to avoid the need to tear down and rebuild the outer
TUN.
This allows us to at least test that our implementation can interoperate
with itself.
Bug: 72950854
Test: this, passing
Merged-In: Ia969f78f4c1a0c0a017f5aad425a68852ff4433a
Change-Id: Ia969f78f4c1a0c0a017f5aad425a68852ff4433a
(cherry picked from commit 144937f3df37ee0b1d5484f10e8c86a8a70a9cb5)
2cb7034baf