Server-side OCSP stapling support.

This is a simpler implementation than OpenSSL's, lacking responder IDs
and request extensions support. This mirrors the client implementation
already present.

Change-Id: I54592b60e0a708bfb003d491c9250401403c9e69
Reviewed-on: https://boringssl-review.googlesource.com/5700
Reviewed-by: Adam Langley <agl@google.com>

ssl/d1_srvr.c

diff --git a/ssl/d1_srvr.c b/ssl/d1_srvr.c
index 3dd7701..ca08651 100644
--- a/ssl/d1_srvr.c
+++ b/ssl/d1_srvr.c
@@ -239,6 +239,16 @@
         s->init_num = 0;
         break;
 
+      case SSL3_ST_SW_CERT_STATUS_A:
+      case SSL3_ST_SW_CERT_STATUS_B:
+        ret = ssl3_send_certificate_status(s);
+        if (ret <= 0) {
+          goto end;
+        }
+        s->state = SSL3_ST_SW_KEY_EXCH_A;
+        s->init_num = 0;
+        break;
+
       case SSL3_ST_SW_KEY_EXCH_A:
       case SSL3_ST_SW_KEY_EXCH_B:
       case SSL3_ST_SW_KEY_EXCH_C: