Stop treating an ack we are not expecting as a fatal error.

[bzbarsky-apple]

We can get a message with a piggybacked ack for a message we have
already gotten a standalone ack for. In this case we should process
the message, not drop it.

Fixes #7909

Problem

See above

Change overview

See above

Testing

New unit test written to cover this case. Fails without the code changes, passes with.

[github-actions]

Size increase report for "gn_qpg-example-build" from 0ade2d5

File	Section	File	VM
chip-qpg6100-lighting-example.out	.text	-16	-16

Full report output

BLOAT REPORT

Files found only in the build output:
    report.csv

Comparing ./master_artifact/chip-qpg6100-lighting-example.out.map and ./pull_artifact/chip-qpg6100-lighting-example.out.map:

BLOAT EXECUTION FAILED WITH CODE 1:
bloaty: unknown file type for file './pull_artifact/chip-qpg6100-lighting-example.out.map'

Comparing ./master_artifact/chip-qpg6100-lighting-example.out and ./pull_artifact/chip-qpg6100-lighting-example.out:

sections,vmsize,filesize
[Unmapped],0,16
.debug_str,0,3
.debug_frame,0,-8
.text,-16,-16
.debug_line,0,-57
.debug_ranges,0,-64
.debug_loc,0,-94
.debug_info,0,-232

[github-actions]

Size increase report for "nrfconnect-example-build" from 0ade2d5

File	Section	File	VM
chip-lock.elf	text	-16	-16
chip-shell.elf	text	-16	-16

Full report output

BLOAT REPORT

Files found only in the build output:
    report.csv

Comparing ./master_artifact/chip-lock.elf and ./pull_artifact/chip-lock.elf:

sections,vmsize,filesize
.debug_frame,0,-8
text,-16,-16
.debug_line,0,-56
.debug_ranges,0,-64
.debug_loc,0,-92
.debug_info,0,-228

Comparing ./master_artifact/chip-shell.elf and ./pull_artifact/chip-shell.elf:

sections,vmsize,filesize
.debug_frame,0,-8
text,-16,-16
.debug_line,0,-56
.debug_ranges,0,-64
.debug_loc,0,-92
.debug_info,0,-124

[github-actions]

Size increase report for "esp32-example-build" from 0ade2d5

File	Section	File	VM
chip-all-clusters-app.elf	.flash.text	-20	-20

Full report output

BLOAT REPORT

Files found only in the build output:
    report.csv

Comparing ./master_artifact/chip-all-clusters-app.elf and ./pull_artifact/chip-all-clusters-app.elf:

sections,vmsize,filesize
[Unmapped],0,20
.debug_frame,0,-16
.flash.text,-20,-20
.debug_ranges,0,-64
.debug_loc,0,-72
.debug_line,0,-97
.debug_str,0,-119
.debug_info,0,-400