USB: rndis_host, various cleanups

Cleanups to the rndis_host code, and a tweak that helps talking to
PXA hardware.  Mostly from Ole André Vadla Ravnås <oleavr@gmail.com>

  - Prevent SET_INTERFACE requests, they give PXA hardware bad indigestion
  - For paranoia, null a pointer after freeing its data
  - Wrap up ActiveSync oddities for RNDIS_QUERY in one routine
  - Use that wrapper when getting the Ethernet address
  - Whitespace fixes

Plus add a comment noting the open issues about some RNDIS clients still
needing TBD kinds of browbeating to accept non-jumbogram packets.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>