Fix for issue #773 - Numlock not sync'ed

I found that mstsc seems to respond to a server TsControlPDU, TS_PDUTYPE_DATAPDU Granted Control message by sending an additional sequence of TsInputPDU packets to ensure that the toggled key states are set correctly. Doing the same with xfreerdp seems to fix the issue, obviously something similar needs to be done for the other supported FreeRDP platforms, but I cannot do this