bnx2x: fix L2-GRE TCP issues

When configuring GRE tunnel using OVS, tcp stream is distributed over
all RSS queues which may cause TCP reordering. It happens since OVS
uses L2GRE protocol when kernel gre uses IPGRE.
Patch defaults gre tunnel to L2GRE which allows proper RSS for L2GRE
packets and (implicitly) disables RSS for IPGRE traffic.

Signed-off-by: Dmitry Kravkov <dmitry@broadcom.com>
Signed-off-by: Ariel Elior <ariele@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>