BLE: write size first when writing an eeprom message

[paul-szczepanek-arm]

Description

When writing an ndef message into eprom the bytes were being written before setting the size - thus resulting in a truncated message. This fix sets the size first and writes the bytes later. Verified using the example nfceeprom app.

Pull request type

[x] Fix
[ ] Refactor
[ ] Target update
[ ] Functionality change
[ ] Docs update
[ ] Test update
[ ] Breaking change

[NirSonnenschein]

/morph build

[mbed-ci]

Build : SUCCESS

Build number : 3419
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/8483/

Triggering tests

/morph test
/morph export-build
/morph mbed2-build

[mbed-ci]

Exporter Build : SUCCESS

Build number : 3043
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/8483/

[mbed-ci]

Test : SUCCESS

Build number : 3213
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/8483/3213