i40e: Do not enable NAPI on q_vectors that have no rings

[ Upstream commit 13a8cd191a2b470cfd435b3b57dbd21aa65ff78c ]

When testing the epoll w/ busy poll code I found that I could get into a
state where the i40e driver had q_vectors w/ active NAPI that had no rings.
This was resulting in a divide by zero error.  To correct it I am updating
the driver code so that we only support NAPI on q_vectors that have 1 or
more rings allocated to them.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>