net: TestIPv6LinkLocalUnicastUDP fails under DragonFly BSD

[4a6f656c]

The "udp" to IPv6 unicast address on the loopback interface test currently
fails under DragonFly BSD, since it returns a local address of 0.0.0.1, rather than an
IPv6 address with zone identifier:

--- FAIL: TestIPv6LinkLocalUnicastUDP (0.00 seconds)
udp_test.go:235: got 0.0.0.1:1221; expected a proper address with
        zone identifier

This requires further investigation, however is likely a DragonFly bug/behaviour.

[4a6f656c]

Comment 1:

This issue was updated by revision 18019df.

LGTM=mikioh.mikioh
R=golang-codereviews, mikioh.mikioh
CC=golang-codereviews
https://golang.org/cl/71500044

[mikioh]

Comment 2:

Labels changed: added repo-main, release-none.

[mikioh]

Merged into #10764.