netfilter: nft_reject_bridge: remove unnecessary ttl set

In the nft_reject_br_send_v4_tcp_reset(), a ttl is set by the
nf_reject_iphdr_put(). so, below code is unnecessary.

Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>