ath9k: Fix up hardware mode and beacons with multiple vifs.

When using a mixture of AP and Station interfaces,
the hardware mode was using the type of the
last VIF registered.  Instead, we should keep track
of the number of different types of vifs and set the
mode accordingly.

In addtion, use the vif type instead of hardware opmode
when dealing with beacons.

Attempt to move some of the common setup code into smaller
methods so we can re-use it when changing vif mode as
well as adding/deleting vifs.

Signed-off-by: Ben Greear <greearb@candelatech.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>