Document Channel ID functions and a few random extras.

Change-Id: I34a6352d265615ee08bb18fd537acf70a558f014
Reviewed-on: https://boringssl-review.googlesource.com/5940
Reviewed-by: Adam Langley <agl@google.com>

ssl/ssl_file.c

diff --git a/ssl/ssl_file.c b/ssl/ssl_file.c
index 95deaae..25e1cc1 100644
--- a/ssl/ssl_file.c
+++ b/ssl/ssl_file.c
@@ -624,4 +624,12 @@
   return ret;
 }
 
+void SSL_CTX_set_default_passwd_cb(SSL_CTX *ctx, pem_password_cb *cb) {
+  ctx->default_passwd_callback = cb;
+}
+
+void SSL_CTX_set_default_passwd_cb_userdata(SSL_CTX *ctx, void *data) {
+  ctx->default_passwd_callback_userdata = data;
+}
+
 IMPLEMENT_PEM_rw(SSL_SESSION, SSL_SESSION, PEM_STRING_SSL_SESSION, SSL_SESSION)