iwlwifi: pcie: set RB size according to user settings

RB size can be configured by user to be greater than 4K.
That's needed for monitor to capture big AMSDUs.
The firmware now enables different RB sizes configuration
via context info.

Signed-off-by: Shaul Triebitz <shaul.triebitz@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>