I recently tried to update some of my BL685c G7 blades and BL465c G7 blades from ESXi 5.1 to 5.5. These all have Emulex OneConnect 10Gb NICs in them. After a successful upgrade, upon reboot it appeared that some of the vmnic interfaces had vanished (the ones that all my virtual machine traffic was on, fortunately the management network was still intact).
Apparently a new driver model has been introduced as part of ESXi 5.5 and the host was now using the elxnet driver which apparently is where the problems started. I tried the usual troubleshooting methods of updating the Emulex firmware to the latest from HP and the latest native Emulex NIC driver available from VMware (which was newer than the one on HP's ESXi 5.5 custom ISO) but the problems continued.
I even wasted a few hours doing a fresh install and setup thinking that it was a bad upgrade. Still no success.
Then, after an extensive Google search and a stop on the VMware Communities site, I came across the following thread:
A poster on that thread had the idea to deactivate the native driver and enable the legacy driver which apparently is still included in the ESXi 5.5 install, and the problem stopped and all of my network adapters were back to normal.
Run the following commands directly on the host to disable the native driver and enable the legacy driver:
esxcli system module set --enabled=false --module=elxnet
esxcli system module set --enabled=true --module=be2net
Then reboot the host. Everything should be back to normal.