web: support Host 100.100.100.100:80 in tailscaled web server

This makes the web server running inside tailscaled on 100.100.100.100:80 support requests with `Host: 100.100.100.100:80` and its IPv6 equivalent.

Prior to this commit, the web server replied to such requests with a redirect to the node's Tailscale IP:5252.

Fixes https://github.com/tailscale/tailscale/issues/14415

Signed-off-by: Alex Klyubin <klyubin@gmail.com>

client/web/web_test.go

@@ -1177,6 +1177,16 @@ func TestRequireTailscaleIP(t *testing.T) {
 			target:      "http://[fd7a:115c:a1e0::53]/",
 			wantHandled: false,
 		},
+		{
+			name:        "quad-100:80",
+			target:      "http://100.100.100.100:80/",
+			wantHandled: false,
+		},
+		{
+			name:        "ipv6-service-addr:80",
+			target:      "http://[fd7a:115c:a1e0::53]:80/",
+			wantHandled: false,
+		},
 	}
 
 	for _, tt := range tests {