mirroring of dispersion parameters for tags not working

[k-doering-NOAA]

Thanks to Yukio for finding this!

Rick says:
The overdisp line is commented out. This happened when the overdisp calculations got moved to ss_objfun. Then when I added mirroring to all the other tag parameters inside of ss_tagrecap, I forgot to also do mirroring for the overdisp. This will be a very quick fix and I will include it in 3.30.19.