Fix QTcpServer::listen() returning true when the port is in use on OS X.

Fix QTcpServer::listen() returning true when the port is in use on OS X.

Way back in the mists of time, someone added SO_REUSEPORT to socket binding,
which was great, because otherwise it meant that multiple UDP sockets couldn't
share the same port on OS X (as platforms with SO_REUSEPORT apparently don't
support rebinding with SO_REUSEADDR).

However: SO_REUSEPORT also means that *any* bind on a port will succeed, which
is most definitely not wanted in the case of TCP sockets, so check the socket
type before performing the actual bind.

Also test that multiple listens don't take effect.

Change-Id: I2f8d450bcfb8a7f3abd8918a4e789a850281dd13
Done-with: Thiago Macieira
Done-with: Shane Kearns
Task-number: QTBUG-6305
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Shane Kearns <shane.kearns@accenture.com>