Don't reset ExchangeContext's "waiting to send" state when sending standalone ack.

[bzbarsky-apple]

This state is meant to track app-level sends, and standalone acks are
not app-level.

Problem

Standalone acks are being treated as "message send", necessitating workarounds in other places (e.g. in exchange context closing logic).

Change overview

Be more careful about what we treat as a "message send" so we can avoid the workarounds in the future.

Testing

Passes CI. Will keep doing that as the workarounds are removed.

[github-actions]

Size increase report for "gn_qpg-example-build" from a70c659

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
.debug_info,0,3442
.debug_loc,0,72
.debug_line,0,49
.debug_str,0,33
.debug_abbrev,0,16
.debug_ranges,0,16
.text,16,16
[Unmapped],0,-16

[github-actions]

Size increase report for "nrfconnect-example-build" from a70c659

File	Section	File	VM
chip-lock.elf	text	16	16
chip-shell.elf	text	12	12
chip-shell.elf	device_handles	-12	-12

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_info,0,3406
.debug_loc,0,73
.debug_line,0,50
.debug_str,0,31
.debug_abbrev,0,16
.debug_ranges,0,16
text,16,16

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

sections,vmsize,filesize
.debug_info,0,814
.debug_loc,0,73
.debug_line,0,50
.debug_str,0,31
.debug_abbrev,0,16
.debug_ranges,0,16
text,12,12
device_handles,-12,-12

[github-actions]

Size increase report for "esp32-example-build" from a70c659

File	Section	File	VM
chip-shell.elf	.flash.text	24	24
chip-all-clusters-app.elf	.flash.text	24	24
chip-lock-app.elf	.flash.text	-40	-40
chip-temperature-measurement-app.elf	.flash.text	-36	-36

Full report output

BLOAT REPORT

Files found only in the build output:
    report.csv

Comparing ./master_artifact/chip-pigweed-app.elf and ./pull_artifact/chip-pigweed-app.elf:

sections,vmsize,filesize

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

sections,vmsize,filesize
.debug_info,0,819
.debug_line,0,115
.debug_loc,0,89
.debug_abbrev,0,36
.debug_str,0,29
.flash.text,24,24
[Unmapped],0,-24

Comparing ./master_artifact/chip-persistent-storage.elf and ./pull_artifact/chip-persistent-storage.elf:

sections,vmsize,filesize

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

sections,vmsize,filesize
.debug_info,0,4095
.debug_line,0,115
.debug_loc,0,93
.debug_abbrev,0,36
.debug_str,0,33
.flash.text,24,24
[Unmapped],0,-24

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

sections,vmsize,filesize
.debug_info,0,3410
.debug_line,0,115
.debug_loc,0,90
[Unmapped],0,40
.debug_abbrev,0,36
.debug_str,0,33
.flash.text,-40,-40

Comparing ./master_artifact/chip-temperature-measurement-app.elf and ./pull_artifact/chip-temperature-measurement-app.elf:

sections,vmsize,filesize
.debug_info,0,3303
.debug_line,0,115
.debug_loc,0,101
.debug_abbrev,0,36
[Unmapped],0,36
.debug_str,0,33
.flash.text,-36,-36

[bzbarsky-apple]

@jmartinez-silabs @LuDuda @jepenven-silabs @msandstedt @saurabhst @Damian-Nordic please take a look?