zd1211rw: move set_rts_cts_work to bss_info_changed

As bss_info_changed may sleep, we can as well set RTS_CTS register right away.
Keep mac->short_preamble for later use (hw reset).

Signed-off-by: Jussi Kivilinna <jussi.kivilinna@mbnet.fi>
Signed-off-by: John W. Linville <linville@tuxdriver.com>