rtl8192u: don't trample on <linux/ieee80211.h> struct namespace

In order to start reducing the duplicated code/constants/macros in this
driver, we need to include <linux/ieee80211.h> to provide the defacto
versions.  However this driver has structs with the same name as the
ones in the main include, so namespace collision prevents us from doing
step #1.

Since the structs actually differ in their respective fields, we can't
simply delete the local ones without impacting the runtime; a conversion
to use the global ones can be considered at a later date if desired.

Rename the ones here with a vendor specific prefix so that we won't have
the namespace collision, and hence can continue on with the cleanup.

Automated conversion done with:

    for i in `find . -name '*.[ch]'` ; do \
      sed -i 's/struct ieee80211_hdr/struct rtl_80211_hdr/g' $i ; \
    done

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>