net/enic: avoid error message when no advanced filtering

net/enic: avoid error message when no advanced filtering

Probing the availability of Flow Manager API may print the following
error log.

PMD: rte_enic_pmd: Devcmd 88 failed with error code -1

The error indicates a flow manager operation failed and happens when
advanced filtering is disabled on vNIC. It is harmless but confusing
to the user. Since advanced filtering is a prerequisite, check first
if it is available and avoid the error message altogether.

Fixes: ea7768b5bba8 ("net/enic: add flow implementation based on Flow Manager API")
Cc: stable@dpdk.org
Signed-off-by: Hyong Youb Kim <hyonkim@cisco.com>
Reviewed-by: John Daley <johndale@cisco.com>