config_opts.h: default osd_recovery_delay_start to 0

This setting was intended to prevent recovery from overwhelming peering traffic
by delaying the recovery_wq until osd_recovery_delay_start seconds after pgs
stop being added to it.  This should be less necessary now that recovery
messages are sent with strictly lower priority then peering messages.

Signed-off-by: Samuel Just <sam.just@inktank.com>
Reviewed-by: Gregory Farnum <greg@inktank.com>