ipv6/tcp: small drop monitor changes

Two kfree_skb() calls must be replaced by consume_skb()
for skbs that are not technically dropped.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>