netfilter: conntrack: fix extension size table

The size table is incorrect due to copypaste error,
this reserves more size than needed.

TSTAMP reserved 32 instead of 16 bytes.
TIMEOUT reserved 16 instead of 8 bytes.

Fixes: 5f31edc0 ("netfilter: conntrack: move extension sizes into core")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>