Stop using the word 'buffer' everywhere.

buffer buffer buffer buffer buffer. At some point, words lose their meaning if
they're used too many times. Notably, the DTLS code can't decide whether a
"buffered message" is an incoming message to be reassembled or an outgoing
message to be (re)transmitted.

Change-Id: Ibdde5c00abb062c603d21be97aff49e1c422c755
Reviewed-on: https://boringssl-review.googlesource.com/8500
Reviewed-by: Adam Langley <agl@google.com>

ssl/d1_lib.c

diff --git a/ssl/d1_lib.c b/ssl/d1_lib.c
index e0853cf..a38d3bb 100644
--- a/ssl/d1_lib.c
+++ b/ssl/d1_lib.c
@@ -270,7 +270,7 @@
   }
 
   dtls1_start_timer(ssl);
-  return dtls1_retransmit_buffered_messages(ssl);
+  return dtls1_retransmit_outgoing_messages(ssl);
 }
 
 static void get_current_time(const SSL *ssl, struct timeval *out_clock) {