Cellular: add callback API

[ghost]

Description

Network connection status callback API added

Pull request type

• Fix

[ghost]

@AnttiKauppila @juhoeskeli please review

[0xc0170]

/morph build

[AnttiKauppila]

Even if this looks like an API change it is not. AT_CellularNetwork already implements these functions, and these functions are inherited from NetworkInterface. CellularNetwork is between of these classes and should inherit same functions.

[mbed-ci]

Build : SUCCESS

Build number : 1414
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/6329/

Triggering tests

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

[0xc0170]

Even if this looks like an API change it is not. AT_CellularNetwork already implements these functions, and these functions are inherited from NetworkInterface. CellularNetwork is between of these classes and should inherit same functions.

This means this is a fix, not a feature as stated above

[mbed-ci]

Test : SUCCESS

Build number : 1198
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/6329/1198

[mbed-ci]

Exporter Build : SUCCESS

Build number : 1063
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/6329/