iwl3945: disable hw scan by default

After new NetworkManager 0.8.996 changes, hardware scanning is causing
microcode errors as reported here:
https://bugzilla.redhat.com/show_bug.cgi?id=683571
and sometimes kernel crashes:
https://bugzilla.redhat.com/show_bug.cgi?id=688252

Also with hw scan there are very bad performance on some systems
as reported here:
https://bugzilla.redhat.com/show_bug.cgi?id=671366

Since Intel no longer supports 3945, there is no chance to get proper
firmware fixes, we need workaround problems by disable hardware scanning
by default.

Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>