ethernet/cavium: use core min/max MTU checking

liquidio: min_mtu 68, max_mtu 16000

thunder: min_mtu 64, max_mtu 9200

CC: netdev@vger.kernel.org
CC: Sunil Goutham <sgoutham@cavium.com>
CC: Robert Richter <rric@kernel.org>
CC: Derek Chickles <derek.chickles@caviumnetworks.com>
CC: Satanand Burla <satananda.burla@caviumnetworks.com>
CC: Felix Manlunas <felix.manlunas@caviumnetworks.com>
CC: Raghu Vatsavayi <raghu.vatsavayi@caviumnetworks.com>
Signed-off-by: Jarod Wilson <jarod@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>