gethostbyname must reject empty name

[VeijoPesonen]

Considers both versions - synchronous and asynchronous. Earlier the
underlying stack was trusted to do this check.

Makes UDPSOCKET_SENDTO_INVALID part of the netsocket extended test set

Description

Greentea test cases TCPSOCKET_CONNECT_INVALID and UDPSOCKET_SENDTO_INVALID do fail without this modification. The issue was hidden due to the fact that TCPSOCKET_CONNECT_INVALID is part of the netsocket extended test set. The extended cases are not run in CI.

UDPSOCKET_SENDTO_INVALID was missing from the extended test set - fixed.

Pull request type

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

[VeijoPesonen]

@SeppoTakalo, @kjbracey-arm and @mikaleppanen please review.

[0xc0170]

/morph build

[mbed-ci]

Build : SUCCESS

Build number : 2194
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/7054/

Triggering tests

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

[mbed-ci]

Exporter Build : SUCCESS

Build number : 1821
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/7054/

[mbed-ci]

Test : SUCCESS

Build number : 1985
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/7054/1985