shadowsocks-libev: fix enumerating server and ss_redir sections

The issue existed since the first revision of the rewrite and was
exposed by commit 4024d4f2

 (luci-base: switch to ubus uci operations)

A quick scan of the current repo indicates that these are the only sites
of wrong call pattern

Fixes openwrt/packages#6113

Signed-off-by: Yousong Zhou <yszhou4tech@gmail.com>