net: Add header for usage of fls64()

[ Upstream commit 8681ef1f ]

Fixes: 3b89ea9c ("net: Fix for_each_netdev_feature on Big endian")
Suggested-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Change-Id: I2cf4fde727392816f7691d31ba74a33fee6a8ddc