discovery: fix num of allowed listeners #712

Job	Run time
build-ceph	2m 17s
build	10m 9s
discovery (container)	3m 56s
discovery (embedded)	3m 45s
demo	4m 10s
ha (sanity)	3m 57s
pytest (cli)	2m 12s
ha (state_transitions)	3m 26s
pytest (cli_change_lb)	2m 47s
ha (state_transitions_both_gws)	4m 29s
pytest (state)	2m 19s
ha (state_transitions_loop)	11m 43s
pytest (multi_gateway)	2m 48s
ha (state_transitions_rand_loop)	14m 58s
pytest (server)	2m 52s
ha (late_registration)	3m 42s
pytest (grpc)	3m 8s
ha (late_registration_loop)	14m 57s
pytest (omap_lock)	4m 27s
ha (4gws)	5m 49s
pytest (old_omap)	2m 19s
ha (4gws_loop)	7m 6s
pytest (log_files)	3m 57s
ha (namespaces)	9m 52s
pytest (nsid)	4m 58s
ha (namespaces_loop)	17m 9s
push-to-registry	0s
	2h 33m 12s

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