skbuff: replace a BUG_ON() with the new DEBUG_NET_WARN_ON_ONCE()

Very few drivers actually have Kconfig knobs for adding
-DDEBUG. 8 according to a quick grep, while there are
93 users of skb_checksum_none_assert(). Switch to the
new DEBUG_NET_WARN_ON_ONCE() to catch bad skbs.

Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20220511172305.1382810-1-kuba@kernel.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>