mac80211: decrease IBSS creation latency

Sufficient scans (at least 2 or 3) should have been done within 7
seconds to find an existing IBSS to join.  This should improve IBSS
creation latency; and since IBSS merging is still in effect, shouldn't
have detrimental effects on eventual IBSS convergence.

Signed-off-by: Dan Williams <dcbw@redhat.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>