SSH: SshKeyExchangeInit is a struct.

Use 'struct' keyword in forward declaration to avoid compiler warning.

Change-Id: I5a10eabea806ce138aed31e8b1a99567afe92e77
Reviewed-by: Christian Kandeler <christian.kandeler@theqtcompany.com>

src/libs/ssh/sshkeyexchange_p.h

@@ -45,7 +45,7 @@ class HashFunction;
 namespace QSsh {
 namespace Internal {
 
-class SshKeyExchangeInit;
+struct SshKeyExchangeInit;
 class SshSendFacility;
 class SshIncomingPacket;