vswitchd: Separate disable system and route.

vswitchd: Separate disable system and route.

Previously, '--disable-system' disables both system dp and the system
routing table.  The patch makes '--disable-system' only disable system
dp and adds '--disable-system-route' for disabling the route table.
This fixes failures when 'make check-system-userspace' for tunnel cases.

As a consequence, hitting errors due to OVS userspace parses the IGMP packet
but its datapaths do not, so odp_flow_key_to_flow() return ODP_FIT_TOO_LITTLE.
commit c645550bb249 ("odp-util: Always report ODP_FIT_TOO_LITTLE for IGMP.")
Fix it by filtering out the IGMP-related error message.

Signed-off-by: William Tu <u9012063@gmail.com>
Signed-off-by: Yi-Hung Wei <yihung.wei@gmail.com>
Co-authored-by: Yi-Hung Wei <yihung.wei@gmail.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>