Travis: Require the macOS IPv6 chutney job

The job was previously set to fast_finish / allow_failure, to
speed up the build.

Closes ticket 33195.

.travis.yml

@@ -100,8 +100,10 @@ matrix:
     - env: RUST_VERSION="nightly" RUST_OPTIONS="--enable-rust --enable-cargo-online-mode"
       compiler: clang
       os: osx
-    - env: CHUTNEY="yes" CHUTNEY_ALLOW_FAILURES="2" SKIP_MAKE_CHECK="yes" CHUTNEY_MAKE_TARGET="test-network-ipv6"
-      os: osx
+    ## Since we're actively developing IPv6, we want to require the IPv6
+    ## chutney tests
+    #- env: CHUTNEY="yes" CHUTNEY_ALLOW_FAILURES="2" SKIP_MAKE_CHECK="yes" CHUTNEY_MAKE_TARGET="test-network-ipv6"
+    #  os: osx
 
 ## (Linux only) Use a recent Linux image (Ubuntu Bionic)
 dist: bionic

changes/ticket33195

+  o Testing:
+    - Stop allowing the Chutney IPv6 Travis job to fail. This job was
+      previously configured to fast_finish (which requires allow_failure), to
+      speed up the build. Closes ticket 33195.