ipw2100: interface-up carrier state fix

From: Imre Deak <imre.deak@nokia.com>

I had a problem where doing an open after a close left the device
unusable. netif_carrier_on should be called whenever we go to the
associated state, but this is not so in case of a close->open sequence.

Signed-off-by: Jiri Benc <jbenc@suse.cz>