ixgbe: move v_idx into q_vector and use as index only

The v_idx value was being used as both a bitmask and an index.  This change
makes it so that the q_vector contains the index and allows for much of the
code to be simplified since disabling a q_vector involves only clearing one
bit in the interrupt bitmask.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>