修复某些情况下引入的default字段污染变量

[wray-lee]

Error: Could not resolve hostname: Name does not resolve
add rule inet shellcrash input ip saddr {default, 10.17.1.0/24, 192.0.0.1, 192.0.0.2, 192.168.150.0/23} accept
                                         ^^^^^^^
Error: Could not resolve hostname: Name does not resolve
add rule inet shellcrash prerouting_dns ip saddr != {default, 10.17.1.0/24, 192.0.0.1, 192.0.0.2, 192.168.150.0/23} return
                                                     ^^^^^^^
Error: Could not resolve hostname: Name does not resolve
add rule inet shellcrash prerouting ip saddr != {default, 10.17.1.0/24, 192.0.0.1, 192.0.0.2, 192.168.150.0/23} return

使用过程中遇到变量过滤不全的问题