Use typedefs for PSK, NPN, ALPN callback functions

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/2052)
diff --git a/ssl/statem/statem_clnt.c b/ssl/statem/statem_clnt.c
index 82713d2..9fa16b1 100644
--- a/ssl/statem/statem_clnt.c
+++ b/ssl/statem/statem_clnt.c
@@ -2204,18 +2204,18 @@
         SSLerr(SSL_F_TLS_PROCESS_CERT_STATUS_BODY, SSL_R_LENGTH_MISMATCH);
         return 0;
     }
-    s->tlsext_ocsp_resp = OPENSSL_malloc(resplen);
-    if (s->ext.ocsp_resp == NULL) {
+    s->ext.ocsp.resp = OPENSSL_malloc(resplen);
+    if (s->ext.ocsp.resp == NULL) {
         *al = SSL_AD_INTERNAL_ERROR;
         SSLerr(SSL_F_TLS_PROCESS_CERT_STATUS_BODY, ERR_R_MALLOC_FAILURE);
         return 0;
     }
-    if (!PACKET_copy_bytes(pkt, s->ext.ocsp_resp, resplen)) {
+    if (!PACKET_copy_bytes(pkt, s->ext.ocsp.resp, resplen)) {
         *al = SSL_AD_DECODE_ERROR;
         SSLerr(SSL_F_TLS_PROCESS_CERT_STATUS_BODY, SSL_R_LENGTH_MISMATCH);
         return 0;
     }
-    s->ext.ocsp_resplen = resplen;
+    s->ext.ocsp.resp_len = resplen;
 
     return 1;
 }