I followed the guidelines explained in this post to enable suspend and hibernate in Ubuntu 13.10. Resuming from suspend worked, including network devices. But somehow, after resuming from hibernation, the network devices did not.
This issue seems to be caused by bug #1184262. It is not related to the networking as such, but to power management. Network Manager does not get the signal that says the computer is now back up.
The workaround I found was to create a file named /etc/pm/sleep.d/10_resume_network containing
#!/bin/sh #Tell Network Manager that resume was successful case "$1" in thaw) /usr/bin/nmcli nm sleep false ;; esac
Then chmod 775 /etc/pm/sleep.d/10_resume_network
In effect, the script tells Network Manager that the computer has now come out of the sleep mode.
Update 20 April 2014: It seems the above is no more needed with Ubuntu 14.04