Reduce RAM Usage for EFR32MG21 examples

[jmartinez-silabs]

Problem

1. Examples on MG21 fail to compile due to ram overflow again.
2. In Lock_app example, zcl onoff command do not trigger the implemented emberAfPostAttributeChangeCallback

Change overview

Freed up ~4k of RAM

• Reduce some memory pools in LWIP
• Reduce OT CLI TX buffer from 1024B to 512B

Increase lighting app to 13k, like it was already done for Lock app, to prevent some CSR failures due to lack of free heap space.

Fix emberAfPostAttributeChangeCallback definition in lock_app, size argument didn't receive the type change and wasn't overwriting the WEAK declaration

Testing

Manual testing on EFR32MG21 wiht both Lighting and Lock example.
Both now compile

./scripts/examples/gn_efr32_example.sh examples/lock-app/efr32/ out/lock_app BRD4180A
./scripts/examples/gn_efr32_example.sh examples/lighting-app/efr32/ out/lighting_app BRD4180A

Validate the examples are still working using python controller :

connect -ble 3840 73141520 1234

zcl NetworkCommissioning AddThreadNetwork 1234 0 0 operationalDataset=hex:0e080000000000000000000300000b35060004001fffe00208dead00beef00cafe0708fddead00beef00000510f4ed320070e00e24a9297b5606f7ec55030a4f70656e5468726561640102d4af0410ac0f452e791654e26c2957a12075eb0a0c0402a0fff8 breadcrumb=0 timeoutMs=1000

zcl NetworkCommissioning EnableNetwork 1234 0 0 networkID=hex:dead00beef00cafe breadcrumb=0 timeoutMs=1000

close-ble

resolve 0 1234

zcl OnOff Toggle 1234 1 0

00> <detail> [DL] Thread packet RCVD: UDP, len 116
00> <detail> [DL]     src  FD11:22::F983:EFFB:8CBB:D3E7, port 11097
00> <detail> [DL]     dest FD11:22::C1C2:67D3:86B3:9371, port 11097
00> <info  > [IN] Secure transport received message destined to fabric 0, node 0x0000000000000015. Key ID 0
00> <info  > [EM] Received message of type 8 and protocolId 327680 on exchange 39024
00> <detail> [EM] ec id: 39024, Delegate: 0x200128d8
00> <detail> [DMG] ICR moving to [Initialize]
00> <detail> [ZCL] Received Cluster Command: Cluster=6 Command=hx Endpoint=hx
00> <info  > [ZCL] On/Off set value: 1 2
00> <info  > [ZCL] Toggle on/off from 0 to 1
00> <efr32 > Lock Action has been initiated
00> <detail> [DMG] ICR moving to [AddCommand]
00> <detail> [IN] Secure message was encrypted: Msg ID 7
00> <info  > [IN] Sending msg from 0x0000000000000015 to 0x000000000001B669 at utc time: ld msec
00> <info  > [IN] Sending secure msg on generic transport
00> <detail> [DL] Thread packet SENT: UDP, len 122
00> <detail> [DL]     src  FD11:22::C1C2:67D3:86B3:9371, port 11097
00> <detail> [DL]     dest FD11:22::F983:EFFB:8CBB:D3E7, port 11097
00> <info  > [IN] Secure msg send status No Error
00> <detail> [DMG] ICR moving to [   Sending]
00> <detail> [DMG] ICR moving to [Uninitiali]
00> <efr32 > Lock Action has been completed

Fixes #7336

[bzbarsky-apple]

This seems pretty small to me, but maybe it's ok.... Need to support at least incoming message, outgoing message, retransmit buffer, standalone ack. That's for a single message exchange. And assuming that nothing else uses pbufs.

I suspect @tcarmelveilleux has thoughts on this.