Update queues per VNIC in single queue mode.
bp->rx_num_qs_per_vnic is not initialized in the single queue mode.
As a result of this when an interface is reconfigured to single
queue mode from an existing multiqueue mode, bp->rx_num_qs_per_vnic
is not updated to the value of 1. Hence, the driver will try to
access more than one queue resulting in a crash.
This patch fixes it by initializing bp->rx_num_qs_per_vnic in the
single queue mode as well.