Also, if you would like to check for linkstate changes in your hosts you can ssh to the desired host (or via iLO console, etc.) and simply grep for "link" (provides most output) or "linkstate" (provides minimal output, only showing up/down events).
Command Syntax (depending on ESXi host version you may need to modify slightly)
ESXi 4.x
cat /var/log/messages | grep -i link-or-
ESXi 5.x
cat /var/log/vmkernel.log | grep -i link
Here's some example output captured while doing network maintenance:
~ # tail -fv /var/log/messages | grep -i link
Jul 26 16:34:43 shell[372172]: tail -fv /var/log/messages | grep -i link
Jul 26 16:35:52 vmkernel: 1:00:26:20.001 cpu13:4462)<3>qlge 0000:08:00.1: ql_link_down: vmnic5: Link Down.
Jul 26 16:35:52 vobd: Jul 26 16:35:52.540: 87980025771us: [vob.net.vmnic.linkstate.down] vmnic vmnic5 linkstate down.
Jul 26 16:35:52 vmkernel: 1:00:26:20.057 cpu15:4947)sfqosq: del pc member - q_ulink is already NULL, return
Jul 26 16:35:52 vmkernel: 1:00:26:20.057 cpu15:4947)sfqosq: del pc member - q_ulink is already NULL, return
Jul 26 16:35:53 vobd: Jul 26 16:35:53.542: 87981034666us: [esx.problem.net.vmnic.linkstate.down] Physical NIC vmnic5 linkstate is down.
Jul 26 16:38:14 vmkernel: 1:00:28:41.743 cpu8:4455)<3>qlge 0000:08:00.1: ql_link_up: vmnic5: Link Up.
Jul 26 16:38:14 vobd: Jul 26 16:38:14.432: 88121917666us: [vob.net.vmnic.linkstate.up] vmnic vmnic5 linkstate up.
Jul 26 16:38:15 vobd: Jul 26 16:38:15.434: 88122926678us: [esx.clear.net.vmnic.linkstate.up] Physical NIC vmnic5 linkstate is up.
Jul 26 16:39:57 vmkernel: 1:00:30:25.243 cpu0:4947)sfqosq: del pc member - q_ulink is already NULL, return
Jul 26 16:39:58 vmkernel: 1:00:30:25.541 cpu2:4443)<3>qlge 0000:11:00.1: ql_link_down: vmnic7: Link Down.
Jul 26 16:39:58 vobd: Jul 26 16:39:58.224: 88225709691us: [vob.net.vmnic.linkstate.down] vmnic vmnic7 linkstate down.
Jul 26 16:39:59 vobd: Jul 26 16:39:59.226: 88226718868us: [esx.problem.net.vmnic.linkstate.down] Physical NIC vmnic7 linkstate is down.
Jul 26 16:40:58 vmkernel: 1:00:31:26.091 cpu13:4459)<3>qlge 0000:11:00.1: ql_link_up: vmnic7: Link Up.
Jul 26 16:40:58 vobd: Jul 26 16:40:58.890: 88286375827us: [vob.net.vmnic.linkstate.up] vmnic vmnic7 linkstate up.
Jul 26 16:40:59 vobd: Jul 26 16:40:59.892: 88287384684us: [esx.clear.net.vmnic.linkstate.up] Physical NIC vmnic7 linkstate is up.Note: The above example uses the tail command in follow (-f) mode to observe the desired forensics in real-time (i.e. during your change). Alternatively, to review historic linkstate changes that have already happened, then use the cat command first noted at the top of the post.