segtree: fix string data initialisation

segtree: fix string data initialisation

commit 63e3d5953c144abbc4ead2665ad7cec799c4cb64 upstream.

This uses the wrong length.  This must re-use the length of the datatype,
not the string length.

The added test cases will fail without the fix due to erroneous
overlap detection, which in itself is due to incorrect sorting of
the elements.

Example error:
 netlink: Error: interval overlaps with an existing one
 add element inet testifsets simple_wild {  "2-1" } failed.
 table inet testifsets {
      ...       elements = { "1-1", "abcdef*", "othername", "ppp0" }

... but clearly "2-1" doesn't overlap with any existing members.
The false detection is because of the "acvdef*" wildcard getting sorted
at the beginning of the list which is because its erronously initialised
as a 64bit number instead of 128 bits (16 bytes / IFNAMSIZ).

Fixes: 5e393ea1fc0a ("segtree: add string "range" reversal support")
Signed-off-by: Florian Westphal <fw@strlen.de>
Reviewed-by: Pablo Neira Ayuso <pablo@netfilter.org>