Re-add DTLS fuzzer corpus

reland of
  https://webrtc-review.googlesource.com/c/src/+/371661
with an absolute BoringSSL path instead of a relative one

BUG=None

Change-Id: I0f2aef4646b8e7c25ea8e0944889d05baa06bd58
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/371940
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Reviewed-by: Jonas Oreland <jonaso@webrtc.org>
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#43598}

test/fuzzers/BUILD.gn

@@ -108,6 +108,9 @@ webrtc_fuzzer_test("dtls_utils_fuzzer") {
     "../../api:array_view",
     "../../p2p:dtls_utils",
   ]
+
+  # Seed from boringssl DTLS corpus.
+  seed_corpus = "//third_party/boringssl/src/fuzz/dtls_client_corpus"
 }
 
 webrtc_fuzzer_test("vp8_qp_parser_fuzzer") {