flow_dissector: add support for tunnel control flags

Dissect [no]csum, [no]dontfrag, [no]oam, [no]crit flags from skb metadata.
This is a prerequisite for matching these control flags using TC flower.

Suggested-by: Ilya Maximets <i.maximets@ovn.org>
Signed-off-by: Davide Caratti <dcaratti@redhat.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>