Revert "smoketest: dhcpc6: do not increase duid"
Revert "smoketest: dhcpc6: do not increase duid"

This reverts commit 1992d9aed31b6906806635687c2b2d2d52310990.

After commit b4889039 ("smoketest: refactor setUp() for all interface based
testcases") we can now use dynamic duid tests.

vyos/vyos-1x,vyos/vyos-1x,vyos/vyos-1x,vyos/vyos-1x