net: wireless: bcmdhd: Fix dhd_txcomplete() dead lock

For TX packet dhd_prot_hdrpull does nothing other than pull the prot
header from the skb. Use a NULL ifdix pointer to indicate a handling
of tx packet and skip most of the header parsing routine - we don't
need it for TX packet and we can skip extra unnecessary PROP_TXSTATUS
parsing. It will resloved dead lock case because we just exit
dhd_prot_hdrpull for TX path.

Change-Id: Ic41e1c549036baeb0fabfb0be4b8331a4bf60682
Signed-off-by: Dmitry Shmidt <dimitrysh@google.com>