datapath: Kernel flow metadata parsing should be less restrictive

datapath: Kernel flow metadata parsing should be less restrictive

The function flow_metadata_from_nlattrs() is very restrictive
about the ordering and type of metadata attributes that it receives.
This patch will change flow_metadata_from_nlattrs() behavior by
ignoring attributes that it does not understand and allowing them
to be passed in arbitrary order.

Issue #8167

Signed-off-by: Ansis Atteka <aatteka@nicira.com>
Acked-by: Jesse Gross <jesse@nicira.com>