tc: fix ipv6 filter selector attribute for some prefix lengths

tc: fix ipv6 filter selector attribute for some prefix lengths

Wrong TCA_U32_SEL attribute packing if prefixLen AND 0x1f equals 0x1f.
These are  /31, /63, /95 and /127 prefix lengths.

Example:
ip6 dst face:b00f::/31
filter parent b: protocol ipv6 pref 2307 u32
filter parent b: protocol ipv6 pref 2307 u32 fh 800: ht divisor 1
filter parent b: protocol ipv6 pref 2307 u32 fh 800::800 order 2048
key ht 800 bkt 0
  match faceb00f/ffffffff at 24

v2: previous patch was made with a wrong repo

Signed-off-by: Yulia Kartseva <hex@fb.com>