bnxt_en: Reserve resources for RFS.

In bnxt_rfs_capable(), add call to reserve vnic resources to support
NTUPLE.  Return true if we can successfully reserve enough vnics.
Otherwise, reserve the minimum 1 VNIC for normal operations not
supporting NTUPLE and return false.

Also, suppress warning message about not enough resources for NTUPLE when
only 1 RX ring is in use.  NTUPLE filters by definition require multiple
RX rings.

Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>