net/enic: fix filter mode detection

net/enic: fix filter mode detection

vnic_dev_capable_filter_mode() currently fails when
CMD_CAPABILITY(CMD_ADD_FILTER) returns ERR_EPERM. In turn, this
failure causes the driver initialization to fail.

But, firmware may legitimately return ERR_EPERM. For example, VF vNIC
returns ERR_EPERM when it does not support filtering at all. So, treat
ERR_EPERM as "no filtering available" instead of an unexpected error.

Fixes: 322b355f2183 ("net/enic/base: bring NIC interface functions up to date")
Cc: stable@dpdk.org
Signed-off-by: Hyong Youb Kim <hyonkim@cisco.com>
Reviewed-by: John Daley <johndale@cisco.com>