sfc: add module parameter to enable MCDI logging on new functions

As many issues are encountered at probe time, where MCDI logging can't be
 enabled through the sysfs node, this change adds a module parameter
 'mcdi_logging_default', which defaults to false.  When set to true, newly-
 probed functions will have MCDI logging enabled.  The setting can
 subsequently be changed as normal through the sysfs node.

Signed-off-by: Edward Cree <ecree@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>