ixgbe: Add module parameter to allow untested and unsafe SFP+ modules

The X520 family of network devices, with the 82599 chip, support a
small number of Intel-verified SFP+ modules on their NICs.  To maintain
stability and quality, the current devices restrict untested 3rd party
SFP+ modules.

This patch introduces a module parameter for ixgbe to allow these untested
modules at the user's peril.  It also includes a warning to the syslog
alerting users that the modules aren't supported, and results may
vary.

CC: Jesper Dangaard Brouer <hawk@comx.dk>
Signed-off-by: Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>