brcmfmac: Fix msgbuf flow control.

brcmfmac: Fix msgbuf flow control.

Msgbuf flow control was using a function to flow off and on which
was not supported without proptx enabled. Also flow control needs
to be handled per ifidx.

Reviewed-by: Arend Van Spriel <[email protected]>
Reviewed-by: Franky (Zhenhui) Lin <[email protected]>
Reviewed-by: Pieter-Paul Giesberts <[email protected]>
Reviewed-by: Daniel (Deognyoun) Kim <[email protected]>
Signed-off-by: Hante Meuleman <[email protected]>
Signed-off-by: Arend van Spriel <[email protected]>
Signed-off-by: John W. Linville <[email protected]>