schema: Update schema version due to xenserver changes.

Commit 32abfca0 "xenserver: New iface-status external id." and
Commit 40043044 "xenserver: Give tap devices iface-ids.", changed
the way a controller interprets the external_ids column of the
Interface table.  This patch increments the schema version number
to reflect that change.

Requested-by: Pankaj Thakkar <thakkar@nicira.com>