sfc: Fix byte order warnings for ethtool RX filter interface

sparse has got a bit more picky since I last ran it over this.  Add
forced casts for use of ~0 as a big-endian value.  Undo the pointless
optimisation of parameter validation with '|'; using '||' avoids these
warnings.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>