rc: Improve netwait DAD logic

[des]

Summary

Disable if IPv6 is not supported, and instead of 10 seconds, default to
one more than the value of net.inet6.ip6.dad_count.

Fixes: 5ead817c3b7a ("rc: Teach netwait to wait for DAD")

[bz]

Apart from that, thank you for improving it so quickly!

With the change applied I am happy and it can just go in.

libexec/rc/rc.d/netwait

44

netwait_dad_timeout=""

if ! [ "${netwait_dad_timeout}" -ge 1 ]; then
        echo foo
fi

yields

[: : bad number
foo

You probably need a

${netwait_dad_timeout:=0}

or something there.

Was bad before already in case it was unset.

Also ! -ge is -lt

So:

if [ "${netwait_dad_timeout:=0}" -lt 1 ]; then

should work?

[des]

libexec/rc/rc.d/netwait

44

! -ge and -lt are not equivalent, as you yourself demonstrated. The former was deliberately chosen because it will dtrt if the variable is set to something that isn't a number. I just forgot, rather stupidly, to consider the null case.

[des]

rf

[bz]

libexec/rc/rc.d/netwait

44

netwait_dad_timeout="BLAH"
if ! [ "${netwait_dad_timeout:=0}" -ge 1 ]; then
        echo foo
fi

will like a -lt comparison still yield

[: BLAH: bad number
foo

[des]

libexec/rc/rc.d/netwait

44

Both versions will print an error message, but only ! -gt will enter the correct branch.