net: ibmveth: force reconfiguring checksum settings on startup

Commit b9367bf3 ("net: ibmveth: convert to hw_features") accidentally
removed call to ibmveth_set_csum_offload() in ibmveth_probe(). Put the
call back where it was, but with additional error checking provided
by ibmveth_set_features().

Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
[sfr: dev -> netdev]
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>