USB: g_mass_storage: superfluous and missing packets fixed

The mass storage function responded needlessly to a set
configuration packet.  This was a leftover from converting
gadget (file storage gadget) into a composite function.

Moreover, it has failed to respond to get max LUN request.
Adding request queueing made the function work better.

Signed-off-by: Michal Nazarewicz <m.nazarewicz@samsung.com>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>