ice: Add handler for ethtool selftest

This patch adds a handler for ethtool selftest. Selftest includes
testing link, interrupts, eeprom, registers and packet loopback.

Signed-off-by: Anirudh Venkataramanan <anirudh.venkataramanan@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>