Add memory manager set to add_ethernet_interface() of test stack

[mikaleppanen]

Description

Added memory manager set to add_ethernet_interface() of test stack. This allows that EMAC memory manager can be used to allocate EMAC driver memory already after the add_ethernet_interface() call.

Pull request type

[X] Fix
[ ] Refactor
[ ] New target
[ ] Feature
[ ] Breaking change

[cmonr]

/morph build

[mbed-ci]

Build : SUCCESS

Build number : 2054
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/6937/

Triggering tests

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

[mbed-ci]

Exporter Build : SUCCESS

Build number : 1696
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/6937/

[mbed-ci]

Test : SUCCESS

Build number : 1863
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/6937/1863