net/virtio: avoid annoying IOPL error log

net/virtio: avoid annoying IOPL error log

In case of running with not enough capabilities, i.e. running as
non-root user any application linked with DPDK prints the message
about IOPL call failure even if it was just called like
'./testpmd --help'. For example, this breaks most of the OVS unit
tests if it built with DPDK support.

Let's register the virtio driver unconditionally and print error
message while probing the device. Silent iopl() call left in the
constructor to have privileges as early as possible as it was before.

Fixes: 565b85dcd9f4 ("eal: set iopl only when needed")
Cc: stable@dpdk.org
Signed-off-by: Ilya Maximets <i.maximets@samsung.com>
Reviewed-by: David Marchand <david.marchand@redhat.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>