Fix migration

In migration 338d7508968c_vpnaas_peer_address_ was mistake in
usage alter_column's parameter type_.

Closes-Bug: #1238561

Change-Id: I6e0eb8260cf5e8d8f557b174c7985e2f7ca1c912
(cherry picked from commit a272a2838313b56edc1463f6d81a01414b37a78f)
Merge "Fix migration" into milestone-proposed