wlan: Avoid possible information leak in send_btc_nlink_msg

In function send_btc_nlink_msg skb alloc is done but the allocated
memory is not initialized. NLMSG_SPACE is used at many places in this
function which does 4 bytes allignment of the buffer. skb_put
adjusts the tail pointer according to this 4 byte allignment results
in padding some extra bytes. Since these bytes are not initialized
it leads to information leak.

To resolve this issue, initialize the skb with zero after alloc skb.

Change-Id: I9d4d2030927c4aedf8c201bf875741b8c800ee7e
CRs-Fixed: 2288807