AP_HAL_SITL: Add missing const in member functions

Signed-off-by: Patrick José Pereira <patrickelectric@gmail.com>

libraries/AP_HAL_SITL/Scheduler.cpp

@@ -73,7 +73,7 @@ bool Scheduler::in_main_thread() const
  * time (due to the logic in SITL_State::wait_clock) and thus taking
  * the semaphore never times out - meaning we essentially deadlock.
  */
-bool Scheduler::semaphore_wait_hack_required()
+bool Scheduler::semaphore_wait_hack_required() const
 {
     if (pthread_self() != _main_ctx) {
         // only the main thread ever moves stuff forwards

libraries/AP_HAL_SITL/Scheduler.h

@@ -33,7 +33,7 @@ public:
 
     void reboot(bool hold_in_bootloader) override;
 
-    bool interrupts_are_blocked(void) {
+    bool interrupts_are_blocked(void) const {
         return _nested_atomic_ctr != 0;
     }
 
@@ -66,7 +66,7 @@ public:
      * threads.
      */
     // a couple of helper functions to cope with SITL's time stepping
-    bool semaphore_wait_hack_required();
+    bool semaphore_wait_hack_required() const;
 
 private:
     SITL_State *_sitlState;

libraries/AP_HAL_SITL/Semaphores.cpp

@@ -31,7 +31,7 @@ bool Semaphore::give()
     return true;
 }
 
-void Semaphore::check_owner()
+void Semaphore::check_owner() const
 {
     // should probably make sure we're holding the semaphore here....
     if (owner != pthread_self()) {

libraries/AP_HAL_SITL/Semaphores.h

@@ -14,7 +14,7 @@ public:
     bool take(uint32_t timeout_ms) override;
     bool take_nonblocking() override;
 
-    void check_owner();  // asserts that current thread owns semaphore
+    void check_owner() const;  // asserts that current thread owns semaphore
 
 protected:
     pthread_mutex_t _lock;

libraries/AP_HAL_SITL/UARTDriver.h

@@ -117,7 +117,7 @@ private:
     void _check_connection(void);
     static bool _select_check(int );
     static void _set_nonblocking(int );
-    bool set_speed(int speed);
+    bool set_speed(int speed) const;
 
     SITL_State *_sitlState;
     uint64_t _receive_timestamp;

libraries/AP_HAL_SITL/UART_utils.cpp

@@ -35,7 +35,7 @@
 #include <sys/stat.h>
 #include <sys/types.h>
 
-bool HALSITL::UARTDriver::set_speed(int speed)
+bool HALSITL::UARTDriver::set_speed(int speed) const
 {
     if (_fd < 0) {
         return false;