ixgbe: Make ATR recognize IPv6 extended headers

Right now ATR is not handling IPv6 extended headers, so ATR is not
being performed on such packets. Fix that by skipping extended
headers when they are present. This also fixes a problem where
the ATR code was not checking that the inner protocol was actually
TCP before setting up the signature rules. Since the protocol check
is intimately involved with the extended header processing as well,
this all gets fixed together.

Signed-off-by: Mark Rustad <mark.d.rustad@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>