brcmfmac: Move out hdrpull from tx_finalize.

In tx_finalize the hdrpull is performed. For the new protocol
msgbuf this is complex, because it does not use protocol headers
in front of payload anymore and therefor can not determine interface
index in the hdr pulll operation. Move out the hdrpull operation
from tx_finalize to make msgbuf implementation easier.

Reviewed-by: Arend Van Spriel <arend@broadcom.com>
Reviewed-by: Franky (Zhenhui) Lin <frankyl@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Reviewed-by: Daniel (Deognyoun) Kim <dekim@broadcom.com>
Signed-off-by: Hante Meuleman <meuleman@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>