net: Change skb_ensure_writable()'s write_len param to unsigned int type

Both pskb_may_pull() and skb_clone_writable()'s length parameters are of
type unsigned int already. Therefore, change this function's write_len
param to unsigned int type.

Signed-off-by: Liu Jian <liujian56@huawei.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Song Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/bpf/20220416105801.88708-3-liujian56@huawei.com