Revert "iptables: 1.4.21 -> 1.6.0"

This reverts commit b2ac241e, which
upgraded iptables, because it causes connmand to segfault on my machine:

    Jan 05 22:02:06 aching connmand[7866]: Connection Manager version 1.30
    Jan 05 22:02:06 aching audit: NETFILTER_CFG table=filter family=2 entries=27
    Jan 05 22:02:06 aching audit[7866]: SYSCALL arch=c000003e syscall=54 success=yes exit=0 a0=a a1=0 a2=40 a3=103a5b0 items=0 ppid=1 pid=7866 auid=4294967295 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=(none) ses=4294967295 comm="connmand" exe="/nix/store/x7lyis4srvd68lflgnqqmg2bc1fm2whb-connman-1.30/bin/connmand" key=(null)
    Jan 05 22:02:06 aching audit: PROCTITLE proctitle=2F6E69782F73746F72652F78376C796973347372766436386C666C676E71716D6732626331666D327768622D636F6E6E6D616E2D312E33302F7362696E2F636F6E6E6D616E64002D2D636F6E6669673D2F6E69782F73746F72652F37383078797137726367376766306271706A3130306C666238336B69367938762D636F6E6E
    Jan 05 22:02:06 aching audit: NETFILTER_CFG table=mangle family=2 entries=6
    Jan 05 22:02:06 aching audit[7866]: SYSCALL arch=c000003e syscall=54 success=yes exit=0 a0=a a1=0 a2=40 a3=1038c00 items=0 ppid=1 pid=7866 auid=4294967295 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=(none) ses=4294967295 comm="connmand" exe="/nix/store/x7lyis4srvd68lflgnqqmg2bc1fm2whb-connman-1.30/bin/connmand" key=(null)
    Jan 05 22:02:06 aching audit: PROCTITLE proctitle=2F6E69782F73746F72652F78376C796973347372766436386C666C676E71716D6732626331666D327768622D636F6E6E6D616E2D312E33302F7362696E2F636F6E6E6D616E64002D2D636F6E6669673D2F6E69782F73746F72652F37383078797137726367376766306271706A3130306C666238336B69367938762D636F6E6E
    Jan 05 22:02:06 aching audit: NETFILTER_CFG table=nat family=2 entries=5
    Jan 05 22:02:06 aching audit[7866]: SYSCALL arch=c000003e syscall=54 success=yes exit=0 a0=a a1=0 a2=40 a3=1037800 items=0 ppid=1 pid=7866 auid=4294967295 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=(none) ses=4294967295 comm="connmand" exe="/nix/store/x7lyis4srvd68lflgnqqmg2bc1fm2whb-connman-1.30/bin/connmand" key=(null)
    Jan 05 22:02:06 aching audit: PROCTITLE proctitle=2F6E69782F73746F72652F78376C796973347372766436386C666C676E71716D6732626331666D327768622D636F6E6E6D616E2D312E33302F7362696E2F636F6E6E6D616E64002D2D636F6E6669673D2F6E69782F73746F72652F37383078797137726367376766306271706A3130306C666238336B69367938762D636F6E6E
    Jan 05 22:02:06 aching connmand[7866]: Aborting (signal 11) [/nix/store/x7lyis4srvd68lflgnqqmg2bc1fm2whb-connman-1.30/sbin/connmand]
    Jan 05 22:02:06 aching connmand[7866]: ++++++++ backtrace ++++++++
    Jan 05 22:02:06 aching connmand[7866]: +++++++++++++++++++++++++++
    Jan 05 22:02:06 aching systemd[1]: connman.service: Main process exited, code=exited, status=1/FAILURE
    Jan 05 22:02:06 aching systemd[1]: connman.service: Unit entered failed state.
    Jan 05 22:02:06 aching systemd[1]: connman.service: Failed with result 'exit-code'.
    Jan 05 22:02:06 aching systemd[1]: connman.service: Service hold-off time over, scheduling restart.
    Jan 05 22:02:06 aching systemd[1]: Stopped Connection service.

Arrived at through bisection, verified using this commit.