As of VOSS 8.2.0.0 the source IP will be one of the segmented mgmt IP interfaces you will have defined under "show mgmt ip" / "show mgmt interface".
In your case sounds like you should have a mgmt clip IP set for that.
The ability to set the syslog source IP was removed in 8.2.0.0.
Refer to the user guide, Segmented Management section.