Adding server fuzzer for early data.

Since any ALPN mismatch and other cause for early data rejection will
cause the server to revert to the non-early data path, this is safe to
flip on for all the fuzzers.

BUG=76

Change-Id: I573740ef8f455915820943d82247fb6bfc37ae41
Reviewed-on: https://boringssl-review.googlesource.com/14465
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>

fuzz/server.cc

@@ -240,6 +240,7 @@ struct GlobalState {
 
     SSL_CTX_set_alpn_select_cb(ctx, ALPNSelectCallback, nullptr);
     SSL_CTX_set_next_protos_advertised_cb(ctx, NPNAdvertiseCallback, nullptr);
+    SSL_CTX_set_early_data_enabled(ctx, 1);
   }
 
   ~GlobalState() {