Comment 30 for bug 996205

I take it back. The same problem happened with the Atheros wifi card, though it only happened after 8-10 suspend/resume cycles, rather than just 1. But this time, I was able to fix it without rebooting because the problem is not the wireless hardware or driver. It is the ethernet driver:

$ lspci
...
01:00.0 Ethernet controller: Atheros Communications Inc. AR8131 Gigabit Ethernet (rev c0)

As mentioned in a previous post, something is not working as expected with the eth0 interface, resulting in quadrillions of errant packets after a resume from suspend-to-ram. So simply reloading the ethernet driver fixes all the networking problems for both ethernet and wifi:

$ sudo rmmod atl1c
$ sudo modprobe atl1c

I've edited /etc/pm/config.d/unload_modules and added

SUSPEND_MODULES="$SUSPEND_MODULES atl1c"

to see if this fixes the problem. And no, I do not intend to reinstall the Intel 5100 card to see if it works there too.