ipvs: initialize tbl->entries after allocation

tbl->entries is not initialized after kmalloc(), therefore
causes an uninit-value warning in ip_vs_lblc_check_expire()
as reported by syzbot.

Reported-by:  <syzbot+3dfdea57819073a04f21@syzkaller.appspotmail.com>
Cc: Simon Horman <horms@verge.net.au>
Cc: Julian Anastasov <ja@ssi.bg>
Cc: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Acked-by: Julian Anastasov <ja@ssi.bg>
Acked-by: Simon Horman <horms@verge.net.au>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>