Problem: parameters not const where const possible

Solution: add const

src/ctx.cpp

@@ -616,7 +616,9 @@ int zmq::thread_ctx_t::set (int option_, const void *optval_, size_t optvallen_)
     return -1;
 }
 
-int zmq::thread_ctx_t::get (int option_, void *optval_, size_t *optvallen_)
+int zmq::thread_ctx_t::get (int option_,
+                            void *optval_,
+                            const size_t *optvallen_)
 {
     const bool is_int = (*optvallen_ == sizeof (int));
     int *value = static_cast<int *> (optval_);

src/ctx.hpp

@@ -73,7 +73,7 @@ class thread_ctx_t
                        const char *name_ = NULL) const;
 
     int set (int option_, const void *optval_, size_t optvallen_);
-    int get (int option_, void *optval_, size_t *optvallen_);
+    int get (int option_, void *optval_, const size_t *optvallen_);
 
   protected:
     //  Synchronisation of access to context options.

src/options.cpp

@@ -85,7 +85,7 @@ int zmq::do_getsockopt (void *const optval_,
 
 #ifdef ZMQ_HAVE_CURVE
 static int do_getsockopt_curve_key (void *const optval_,
-                                    size_t *const optvallen_,
+                                    const size_t *const optvallen_,
                                     const uint8_t (&curve_key_)[CURVE_KEYSIZE])
 {
     if (*optvallen_ == CURVE_KEYSIZE) {

tests/test_security_curve.cpp

@@ -100,9 +100,9 @@ static void zap_handler_large_routing_id (void * /*unused_*/)
     zap_handler_generic (zap_ok, large_routing_id);
 }
 
-void expect_new_client_curve_bounce_fail (char *server_public_,
-                                          char *client_public_,
-                                          char *client_secret_,
+void expect_new_client_curve_bounce_fail (const char *server_public_,
+                                          const char *client_public_,
+                                          const char *client_secret_,
                                           char *my_endpoint_,
                                           void *server_,
                                           void **client_mon_ = NULL,