Generate Rust wrappers for HKDF

This change exposes the necessary APIs for rust-openssl's HKDF wrappers
in [PKeyCtxRef]
(https://docs.rs/openssl/latest/openssl/pkey_ctx/struct.PkeyCtxRef.html#method.set_hkdf_mode).

Diff of the generated bindings: https://gist.github.com/mauricelam/51602bf17d4a5f9023a27cbe5f9ff705

Change-Id: Ic8df3d5308cfee5964ceadd3c2524b77e12512fb
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/57066
Reviewed-by: Alex Gaynor <alex.gaynor@gmail.com>
Commit-Queue: David Benjamin <davidben@google.com>
Reviewed-by: David Benjamin <davidben@google.com>
diff --git a/rust/wrapper.h b/rust/wrapper.h
index 316cff1..1d65c5a 100644
--- a/rust/wrapper.h
+++ b/rust/wrapper.h
@@ -40,6 +40,7 @@
 #include "../include/openssl/hpke.h"
 #include "../include/openssl/hrss.h"
 #include "../include/openssl/is_boringssl.h"
+#include "../include/openssl/kdf.h"
 #include "../include/openssl/lhash.h"
 #include "../include/openssl/md4.h"
 #include "../include/openssl/md5.h"