Do not have more data in a pipeline than the split_send_fragment

We shouldn't be putting more data into a pipeline than the value of
split_send_fragment.

This is a backport of a fix which was included in a much larger commit in
master (c618679) related to moving the pipelining code into the new
record layer that exists there.

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Hugo Landau <hlandau@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from openssl#20208)

(cherry picked from commit 2c4b1c7)

ssl/record/rec_layer_s3.c

@@ -591,14 +591,13 @@ int ssl3_write_bytes(SSL *s, int type, const void *buf_, size_t len,
         if (numpipes > maxpipes)
             numpipes = maxpipes;
 
-        if (n / numpipes >= max_send_fragment) {
+        if (n / numpipes >= split_send_fragment) {
             /*
              * We have enough data to completely fill all available
              * pipelines
              */
-            for (j = 0; j < numpipes; j++) {
-                pipelens[j] = max_send_fragment;
-            }
+            for (j = 0; j < numpipes; j++)
+                pipelens[j] = split_send_fragment;
         } else {
             /* We can partially fill all available pipelines */
             tmppipelen = n / numpipes;