meson: remove obsolete check for ETH_FLAG_NTUPLE

meson: remove obsolete check for ETH_FLAG_NTUPLE

The ETH_FLAG_NTUPLE constant was introduced to Linux in

  commit 15682bc488d4af8c9bb998844a94281025e0a333
  Author: Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@intel.com>
  Date:   Wed Feb 10 20:03:05 2010 -0800

    ethtool: Introduce n-tuple filter programming support

This is old enough that all our supported platforms can be assumed
to have this feature.

A typo in the existing condition "NTUBLE" instead of "NTUPLE" meant the
code was never enabled in the first place, which is an illustration of
why it is worth eliminating redundant conditional checks.

Reviewed-by: Ján Tomko <jtomko@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>