Expose SSL_max_seal_overhead.

Change-Id: I0626f926cad033a19eeb977e454f3c9293f01fd6
Reviewed-on: https://boringssl-review.googlesource.com/12106
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/include/openssl/ssl.h b/include/openssl/ssl.h
index c83299a..56280a6 100644
--- a/include/openssl/ssl.h
+++ b/include/openssl/ssl.h
@@ -3127,6 +3127,10 @@
  * GREASE. See draft-davidben-tls-grease-01. */
 OPENSSL_EXPORT void SSL_CTX_set_grease_enabled(SSL_CTX *ctx, int enabled);
 
+/* SSL_max_seal_overhead returns the maximum overhead, in bytes, of sealing a
+ * record with |ssl|. */
+OPENSSL_EXPORT size_t SSL_max_seal_overhead(const SSL *ssl);
+
 
 /* Deprecated functions. */