I've seen some tweeks in other post for iscsi, have you tried those ?

it was something like this:
maxRecvDataSegmentLen=65536
MaxBurstLength=16776192
Maxxmitdatasegment=65536

I've also seen posts that states that the initiator and target needs to be set to the same value.

from what you have posted from dmesg, I would suspect a network issue.