Update: the issue seems to affect only Citrix Netscaler on FreeBSD. Other operating systems seem not affected.
Do not install ESXi updates with a release date of 15 October 2014. Virtual machines with E1000 network interface cards will disconnect from the network.
This issue has been reported by multiple VMware customers in this VMware communities thread.
To resolve the issue, rollback to a previous version of ESXi. This can be done by rebooting the ESXi host, press Shift+R. The procedure is explained here.
After installing the updates, the build is reported as v5.5.0 2143827.
The working build based on ESXi 5.5.0 Update 2 is 206190
The image below shows the affected patches.