BUG/MINOR: resolvers/mworker: missing default resolvers in mworker mode

BUG/MINOR: resolvers/mworker: missing default resolvers in mworker mode

Since commit fe75c1e12da061 ("MEDIUM: startup: remove
MODE_MWORKER_WAIT") the MODE_MWORKER_WAIT constant disappeared. The
initialization of the default resolvers section was conditionned by this
constant.

The section must be created in mworker mode, but only in the worker not in
the master. It was currently completely disabled in both the master and
the worker which could break configuration using it, as well as the
httpclient.

No backport needed.