ipw2x00: replace "ieee80211" with "libipw" where appropriate

"ieee80211" was the old name of the common library for ipw2100 and
ipw2200.  It was renamed to "libipw", but some occurrences of the old
name remained.

Rename alloc_ieee80211() to alloc_libipw() and free_ieee80211() to
free_libipw().  Adjust comments and label names.  Change prefixes in
diagnostic messages.

Keep /proc/net/ieee80211 under the original name to avoid breaking user
interface.

Move the affected EXPORT_SYMBOL macros to their proper places.

Signed-off-by: Pavel Roskin <proski@gnu.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>