net: Fix for_each_netdev_feature on Big endian

The features attribute is of type u64 and stored in the native endianes on
the system. The for_each_set_bit() macro takes a pointer to a 32 bit array
and goes over the bits in this area. On little Endian systems this also
works with an u64 as the most significant bit is on the highest address,
but on big endian the words are swapped. When we expect bit 15 here we get
bit 47 (15 + 32).

This patch converts it more or less to its own for_each_set_bit()
implementation which works on 64 bit integers directly. This is then
completely in host endianness and should work like expected.

Fixes: fd867d51

 ("net/core: generic support for disabling netdev features down stack")
Signed-off-by: Hauke Mehrtens <hauke.mehrtens@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>