Fix buffer size computation.

The maximum buffer size computation wasn't quite done right in
ssl_buffer.c, so we were failing with BUFFER_TOO_SMALL for sufficiently
large records. Fix this and, as penance, add 103 tests.

(Test that we can receive maximum-size records in all cipher suites.
Also test SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER while I'm here.)

BUG=526998

Change-Id: I714c16dda2ed13f49d8e6cd1b48adc5a8491f43c
Reviewed-on: https://boringssl-review.googlesource.com/5785
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/ssl/test/runner/conn.go b/ssl/test/runner/conn.go
index 42bc840..1b8700c 100644
--- a/ssl/test/runner/conn.go
+++ b/ssl/test/runner/conn.go
@@ -876,7 +876,7 @@
 	isClientHello := typ == recordTypeHandshake && len(data) > 0 && data[0] == typeClientHello
 	for len(data) > 0 || first {
 		m := len(data)
-		if m > maxPlaintext {
+		if m > maxPlaintext && !c.config.Bugs.SendLargeRecords {
 			m = maxPlaintext
 		}
 		if typ == recordTypeHandshake && c.config.Bugs.MaxHandshakeRecordLength > 0 && m > c.config.Bugs.MaxHandshakeRecordLength {