This reverts commit 6f2a0198.

This commit removed error reporting from virNetDevSendEthtoolIoctl
pushing responsibility onto the callers. This is wrong, however,
since virNetDevSendEthtoolIoctl calls virNetDevSetupControl
which can still report errors. So as a result virNetDevSendEthtoolIoctl
may or may not report errors depending on which bit of it fails, and as
a result callers now overwrite some errors.

It also introduced a regression causing unprivileged libvirtd to
spew error messages to the console due to inability to query the
NIC features, an error which was previously ignored.

virNetDevSetupControlFull:148 : Cannot open network interface control socket: Operation not permitted
virNetDevFeatureAvailable:3062 : Cannot get device wlp3s0 flags: Operation not permitted
virNetDevSetupControlFull:148 : Cannot open network interface control socket: Operation not permitted
virNetDevFeatureAvailable:3062 : Cannot get device wlp3s0 flags: Operation not permitted
virNetDevSetupControlFull:148 : Cannot open network interface control socket: Operation not permitted
virNetDevFeatureAvailable:3062 : Cannot get device wlp3s0 flags: Operation not permitted
virNetDevSetupControlFull:148 : Cannot open network interface control socket: Operation not permitted
virNetDevFeatureAvailable:3062 : Cannot get device wlp3s0 flags: Operation not permitted

Looking back at the original posting I see no explanation of why
thsi refactoring was needed, so reverting the clearly broken
error reporting logic looks like the best option.
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>