pdl: Generate just a single length check per chunk

We can now deviate from what ‘bluetooth_packetgen’ generates and thus
simplify our code a little.

Test: atest pdl_tests
(cherry picked from https://android-review.googlesource.com/q/commit:3aee419e5ee741585dde22d530bb40e2c251fc3c)
Merged-In: Ica2cfe4e7d97dab5edfc897d6a2581b36dfb7885
Change-Id: Ica2cfe4e7d97dab5edfc897d6a2581b36dfb7885