net: ipc_router: Fix buffer overflow during memcpy

The increment logic of u64 pointer in skb_copy_to_log_buf() leads to
buffer overflow.

Modify the proto type of skb_copy_to_log_buf() function to accept
only unsigned char pointer.

CRs-Fixed: 2212592
Change-Id: I8affff1316656c1060ec57f2fb10b46f85314358
Signed-off-by: Arun Kumar Neelakantam <aneela@codeaurora.org>