ethdev: read link state interrupt without link update service
ethdev: read link state interrupt without link update service

It is now possible to read link status updated by interrupt without
having manual link_update() service provided by the PMD.
Indeed link_update() is useless in interrupt case. So check of this
function pointer must be done in the interrupt case only.

Signed-off-by: Thomas Monjalon <ee2fa8b2681c737f775687e475dcbf2028a412f1@6wind.com>
Acked-by: Olivier Matz <dfcc1510895413197abb4336e39bb0a3906cba71@6wind.com>

phermansson/dpdk,phermansson/dpdk,phermansson/dpdk,phermansson/dpdk