ixgbevf: Update q_vector to contain ring pointers instead of bitmaps

For most cases the ixgbevf driver will only ever contain a single Tx and
single Rx queue.  In order to track that it makes more sense to use a
pointer instead of using a bitmap which must be search in order to locate
the ring on an adapter index.  As such I am changing the code to use
pointers and an iterator to access all rings on a given q_vector.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: Greg Rose <gregory.v.rose@intel.com>
Tested-by: Sibai Li <sibai.li@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>