brcm80211: smac: remove duplicate definition of D11_PHY_HDR_LEN

The macro definition D11_PHY_HDR_LEN was defined in d11.h and pub.h.
It has been removed from pub.h.

Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Reviewed-by: Roland Vossen <rvossen@broadcom.com>
Reviewed-by: Alwin Beukers <alwin@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>