No GCM Push on Wifi

I ran into a problem where one day I noticed that I was no longer receiving GCM push notifications when on wifi on my Android Nexus 5x.  If I disabled wifi and used cellular data, notifications would work fine.  Using the dial code *#*#426#*#* I was able to locate the Google Play Services log console and I saw a bunch of messages like this:

02-04 08:32:35.939 net=1: Failed connection err:24
02-04 08:33:31.329 net=1: Failed connection err:24
02-04 08:33:31.595 net=1: Failed connection err:19
02-04 08:34:22.032 net=1: Failed connection err:24

I thought the problem was my phone but it turns out it was actually my DNS settings for my local network.  After a lot of painstaking work, I found that mtalk.google.com was resolving to 216.239.38.120.  This was because I was using DNS to force Google searches into "safe search" mode.  After adding a DNS entry for mtalk.google.com as 108.177.98.188, all of the sudden my GCM notifications started working again.  Yeah!