pdl: Add Packet_Reserved_Field canonical test

This test was already working, just needed to be added.

Tag: #feature
Bug: 233340330
Test: atest pdl_tests pdl_rust_generator_tests_{le,be}
(cherry picked from https://android-review.googlesource.com/q/commit:fed8932ce6b299c8883a87050c6338860301267f)
Merged-In: I81f0e4c85fa61da9010bfa2a592839a55ae8979a
Change-Id: I81f0e4c85fa61da9010bfa2a592839a55ae8979a