Updates `golang.org/x/net` to master (d11bb6cd).
```
$ go test ./...
ok golang.org/x/net/bpf (cached)
ok golang.org/x/net/context (cached)
ok golang.org/x/net/context/ctxhttp (cached)
? golang.org/x/net/dict [no test files]
ok golang.org/x/net/dns/dnsmessage (cached)
ok golang.org/x/net/html (cached)
ok golang.org/x/net/html/atom (cached)
ok golang.org/x/net/html/charset (cached)
ok golang.org/x/net/http/httpguts (cached)
ok golang.org/x/net/http/httpproxy (cached)
ok golang.org/x/net/http2 (cached)
? golang.org/x/net/http2/h2i [no test files]
ok golang.org/x/net/http2/hpack (cached)
ok golang.org/x/net/icmp 0.199s
ok golang.org/x/net/idna (cached)
? golang.org/x/net/internal/iana [no test files]
? golang.org/x/net/internal/nettest [no test files]
ok golang.org/x/net/internal/socket (cached)
ok golang.org/x/net/internal/socks (cached)
ok golang.org/x/net/internal/sockstest (cached)
ok golang.org/x/net/internal/timeseries (cached)
ok golang.org/x/net/ipv4 (cached)
ok golang.org/x/net/ipv6 (cached)
ok golang.org/x/net/nettest (cached)
ok golang.org/x/net/netutil (cached)
ok golang.org/x/net/proxy (cached)
ok golang.org/x/net/publicsuffix (cached)
ok golang.org/x/net/trace (cached)
ok golang.org/x/net/webdav (cached)
ok golang.org/x/net/webdav/internal/xml (cached)
ok golang.org/x/net/websocket (cached)
ok golang.org/x/net/xsrftoken (cached)
```
Fixes#3692.
Roland Bracewell Shoemaker