b43: fill PHY ctl word1 in TX header for N-PHY

This patch fixes tramissing on OFDM rates for PHYs 1 and 2. There is
still something wrong with PHYs 3+. Tests has shown decreasing of
performance on CCK rates by 1-2%, we have to live with that.
Additionaly this noticeably reduces amount of PHY errors. They were
mostly produced by auto-switching to higher rate for better
performanced, which resulted in no transmit at all and PHY errors.

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>