segtree: copy expr data to closing element

segtree: copy expr data to closing element

When last expr has no closing element we did not propagate
expr properties such as comment or expire date to the newly
allocated set elem.

Before:
nft create table t
nft 'add set t s { type ipv4_addr; flags interval; timeout 60s; }'
nft add element t s { 224.0.0.0/3 }
nft list set t s | grep -o 'elements.*'
elements = { 224.0.0.0-255.255.255.255 }

nft flush set t s
nft add element t s { 224.0.0.0/4, 240.0.0.0/4 }
nft list set t s | grep -o 'elements.*'
elements = { 224.0.0.0/4 expires 55s152ms, 240.0.0.0-255.255.255.255 }

nft delete set t s
nft 'add set t s { type ipv4_addr; flags interval; auto-merge; timeout 60s; }'
nft add element t s { 224.0.0.0/4, 240.0.0.0/4 }
nft list set t s | grep -o 'elements.*'
elements = { 224.0.0.0-255.255.255.255 }

After:
elements = { 224.0.0.0-255.255.255.255 expires 58s515ms }
elements = { 224.0.0.0/4 expires 54s622ms, 240.0.0.0-255.255.255.255 expires 54s622ms }
elements = { 224.0.0.0-255.255.255.255 expires 57s92ms }

Bugzilla: https://bugzilla.netfilter.org/show_bug.cgi?id=1454
Signed-off-by: Florian Westphal <fw@strlen.de>