ethtool: fix ethnl_bitmap32_not_zero() bit interval semantics

ethtool: fix ethnl_bitmap32_not_zero() bit interval semantics

ethnl_bitmap32_not_zero() should return true if some bit in [start, end)
is set:

- Fix inverted memchr_inv() sense: return true when the scan finds a
  non-zero byte, not when the middle words are all zero.
- Return false for an empty interval (end <= start).
- When end is 32-bit aligned, indices in [start, end) do not include any
  bits from map[end_word]; return false after earlier checks found no
  non-zero data.

Fixes: 10b518d4e6dd ("ethtool: netlink bitset handling")
Signed-off-by: Chenguang Zhao <zhaochenguang@kylinos.cn>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>