Fix missing footer space during WiFi provisioning

[mspang]

As of a868187 ("Reduce use of maximum-sized packet buffers (#4434)"),
network provisioning does not allocate enough space to encrypt the WiFi
credentials payload, resulting in the following error:

CHIP:NP: Failed in sending Network Creds. error Error 4047 (0x00000FCF)

Pending API improvements to make these errors less likely, manually add
the needed extra space at allocation time.

Fixes #4823

[github-actions]

Size increase report for "nrfconnect-example-build" from cb845e1

File	Section	File	VM
chip-lock.elf	shell_root_cmds_sections	12	12
chip-lock.elf	text	4	4
chip-lighting.elf	shell_root_cmds_sections	12	12
chip-lighting.elf	text	4	4

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,0,7101
.debug_line,0,641
.debug_abbrev,0,278
.debug_loc,0,68
shell_root_cmds_sections,12,12
text,4,4

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

sections,vmsize,filesize
.debug_info,0,7101
.debug_line,0,645
.debug_abbrev,0,278
.debug_loc,0,72
shell_root_cmds_sections,12,12
text,4,4

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

sections,vmsize,filesize

[github-actions]

Size increase report for "esp32-example-build" from cb845e1

File	Section	File	VM
chip-all-clusters-app.elf	.flash.text	4	4

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

sections,vmsize,filesize
.debug_info,0,5842
.debug_line,0,830
.debug_abbrev,0,322
.debug_loc,0,32
.flash.text,4,4
.xt.prop._ZTVN4chip11DeviceLayer37DeviceNetworkProvisioningDelegateImplE,0,2

[bzbarsky-apple]

This is OK as far as it goes, but:

1. NetworkProvisioning::SendThreadCredentials has the same issue.
2. The uses in BdxTransferSession would have the same issue, if we ever sent that data anywhere.
3. The use in src/app/encoder.cpp would have this issue if it did not ridiculously over-allocate.

Maybe just like we have MessagePacketBuffer we should have MessagePacketBufferWriter, which is automatically little-endian and allocates the footer space?

@kpschoedel

[kpschoedel]

Maybe just like we have MessagePacketBuffer we should have MessagePacketBufferWriter, which is automatically little-endian and allocates the footer space?

On seeing this case, I think PacketBufferWriter is already overspecialized. I think it would be better for it to take ownership of an existing PacketBufferHandle, however allocated, just like PacketBufferTLVWriter.

[bzbarsky-apple]

@kpschoedel That seems fine to me. Want to switch it around, or should I?

[kpschoedel]

PR #4874