UPSTREAM: xtables-compat: fix snprintf truncation warnings

proto is u16 in the data structure, so this gave:
nft-ipv6.c:422:44: warning: '__builtin___snprintf_chk' output may be truncated before the last format character [-Wformat-truncation=]

Signed-off-by: Florian Westphal <fw@strlen.de>
(cherry picked from commit eb358546b04c57a60c023744e815dea173733370)

Test: builds
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I368eb407112ff3ba157c36afe23579b9f849c441
2 files changed