Rename SSL_RENEGOTIATION macro

- new name is more explicit
- avoids collision with POLARSSL_SSL_RENEGOTIATION config flag when prefixing
  will be applied
diff --git a/library/ssl_cli.c b/library/ssl_cli.c
index 1244435..ab9eeed 100644
--- a/library/ssl_cli.c
+++ b/library/ssl_cli.c
@@ -120,7 +120,7 @@
 
     *olen = 0;
 
-    if( ssl->renegotiation != SSL_RENEGOTIATION )
+    if( ssl->renegotiation != SSL_RENEGOTIATION_IN_PROGRESS )
         return;
 
     SSL_DEBUG_MSG( 3, ( "client hello, adding renegotiation extension" ) );
@@ -1195,7 +1195,7 @@
     if( ssl->in_msgtype != SSL_MSG_HANDSHAKE )
     {
 #if defined(POLARSSL_SSL_RENEGOTIATION)
-        if( ssl->renegotiation == SSL_RENEGOTIATION )
+        if( ssl->renegotiation == SSL_RENEGOTIATION_IN_PROGRESS )
         {
             ssl->renego_records_seen++;
 
@@ -1581,21 +1581,21 @@
         handshake_failure = 1;
     }
 #if defined(POLARSSL_SSL_RENEGOTIATION)
-    else if( ssl->renegotiation == SSL_RENEGOTIATION &&
+    else if( ssl->renegotiation == SSL_RENEGOTIATION_IN_PROGRESS &&
              ssl->secure_renegotiation == SSL_SECURE_RENEGOTIATION &&
              renegotiation_info_seen == 0 )
     {
         SSL_DEBUG_MSG( 1, ( "renegotiation_info extension missing (secure)" ) );
         handshake_failure = 1;
     }
-    else if( ssl->renegotiation == SSL_RENEGOTIATION &&
+    else if( ssl->renegotiation == SSL_RENEGOTIATION_IN_PROGRESS &&
              ssl->secure_renegotiation == SSL_LEGACY_RENEGOTIATION &&
              ssl->allow_legacy_renegotiation == SSL_LEGACY_NO_RENEGOTIATION )
     {
         SSL_DEBUG_MSG( 1, ( "legacy renegotiation not allowed" ) );
         handshake_failure = 1;
     }
-    else if( ssl->renegotiation == SSL_RENEGOTIATION &&
+    else if( ssl->renegotiation == SSL_RENEGOTIATION_IN_PROGRESS &&
              ssl->secure_renegotiation == SSL_LEGACY_RENEGOTIATION &&
              renegotiation_info_seen == 1 )
     {