cfg80211: work around a sparse issue

sparse reports:
net/wireless/util.c:499:30: error: cannot size expression
net/wireless/util.c:503:30: error: cannot size expression

This is evidently due to the EXPORT_SYMBOL() of the
bridge_tunnel_header and rfc1042 header variables.
Move them to the end of the file to work around the
sparse issue. The error itself from sparse can be
ignored safely, but since sparse stops parsing at
errors, other issues after this would go undetected.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>