Signed-off-by: Longxiang Lyu <lolv@microsoft.com>

Signed-off-by: Longxiang Lyu <lolv@microsoft.com>

From the ovs doc, if mod-flow is used without --strict, priority is not
used in matching.
This will cause problem for downstream set_drop when
duplicate_nic_upstream is disabled.

For example:

When set_drop is applied to upstream_nic_flow(sonic-net#1), mod-flow will match both
flow sonic-net#2 and flow  sonic-net#3 as priority is not used in flow match.

So let's enforce strict match for mod-flow.

Signed-off-by: Longxiang Lyu <lolv@microsoft.com>