I just tried doing the same thing on a bare metal server with solaris 11.1. I tried everything, and always got stuck with the link busy error. I had the bge NICs onboard, and even tried adding a sun quad gigE card (igb driver). I tried editing the /kernel/drv/igb.conf file and setting the default_mtu as I read in the IGB documentation as well. Still wouldn't work. I assume this is a bug, but I couldn't find anywhere to report it, and since I don't have a support account, I wouldn't be able to get a patch if they did fix it.
Since jumbo frames was required for my fileserver, I gave up and went back to Solaris 10u10. It worked just fine there. All I can say is, good luck. I searched everywhere and tried every suggested trick and nothing worked.