Add ToS option to sockets.

Add ToS option to sockets.

Creates a new SocketOption called called TypeOfServiceOption that can be
used with the existing setSocketOption method to set the ToS byte in a
socket socket. This is done only for unix systems because windows
doesn't support directly setting the ToS/DSCP byte:
http://support.microsoft.com/kb/248611
http://blogs.msdn.com/b/wndp/archive/2006/07/05/657196.aspx

Change-Id: Idf9da2dd8307ac7057982fbfdf9e4e9ebe366780
Task-number: QTBUG-6221
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Peter Hartmann <peter.hartmann@nokia.com>