Try fallback drivers if global init for preferred drivers fails

Try fallback drivers if global init for preferred drivers fails

Driver global init was considered a hard failure. Thus if, for example,
you used the Broadcom STA driver and didn't have nl80211 or cfg80211
loaded into the kernel, and specified a driver value of "nl80211,wext",
the nl80211 driver's global init would fail with the following message:

nl80211: 'nl80211' generic netlink not found
Failed to initialize driver 'nl80211'

but since global init was a hard failure, creating the supplicant
interface would fail and the WEXT driver would not be tried.
Give other drivers a chance instead.

Signed-hostap: Dan Williams <dcbw@redhat.com>
intended-for: hostap-1