users: fix exception during signup for IPv6 addresses.

`ip_address.private?` failed on IPv6 addresses.

app/logical/user_verifier.rb

@@ -23,7 +23,11 @@ class UserVerifier
   end
 
   def is_local_ip?
-    ip_address.loopback? || ip_address.link_local? || ip_address.private? || ip_address.try(:unique_local?)
+    if ip_address.ipv4?
+      ip_address.loopback? || ip_address.link_local? || ip_address.private?
+    elsif ip_address.ipv6?
+      ip_address.loopback? || ip_address.link_local? || ip_address.unique_local?
+    end
   end
 
   def is_logged_in?

test/functional/users_controller_test.rb

@@ -293,9 +293,19 @@ class UsersControllerTest < ActionDispatch::IntegrationTest
         setup do
           @private_ip = "192.168.0.1"
           @valid_ip = "187.37.226.17" # a random valid, non-proxy public IP
+          @valid_ipv6 = "2600:1700:6b0:a518::1"
           @proxy_ip = "51.15.128.1"
         end
 
+        should "work for a public IPv6 address" do
+          self.remote_addr = @valid_ipv6
+
+          post users_path, params: { user: { name: "xxx", password: "xxxxx1", password_confirmation: "xxxxx1" }}
+
+          assert_redirected_to User.last
+          assert_equal(false, User.last.requires_verification)
+        end
+
         should "mark accounts created by already logged in users as requiring verification" do
           self.remote_addr = @valid_ip