fuzz-dhcp6-client: avoid assertion failure on samples which dont fit in pipe

Fixes https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=11584.

src/fuzz/fuzz-dhcp6-client.c

@@ -49,6 +49,9 @@ static void fuzz_client(const uint8_t *data, size_t size, bool is_information_re
 }
 
 int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
+        if (size > 65536)
+                return 0;
+
         /* This triggers client_receive_advertise */
         fuzz_client(data, size, false);
 

src/fuzz/fuzz-dhcp6-client.options

@@ -0,0 +1,2 @@
+[libfuzzer]
+max_len = 65536