Added long echo sequence test to EMAC tests

[mikaleppanen]

Description

Test echoes 50000 random length ethernet frames between CTP echo server and device.

Pull request type

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

[cmonr]

/morph build

[mbed-ci]

Build : SUCCESS

Build number : 2360
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/7208/

Triggering tests

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

[mbed-ci]

Exporter Build : FAILURE

Build number : 1986
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/7208/

[mbed-ci]

Test : SUCCESS

Build number : 2149
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/7208/2149

[0xc0170]

/morph export-build

[mbed-ci]

Exporter Build : SUCCESS

Build number : 1994
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/7208/