net/wireless: ipw2x00: Use IW_HANDLER macro from linux/wireless.h

Use IW_HANDLER macro in ipw2100.c to declare wireless handlers.

Note: ipw2200.c already uses it.

Signed-off-by: Stanislav Yakovlev <stas.yakovlev@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>