param & param_shmem: enable locking

We need to protect access to the param_values array. This is dynamically
allocated and resized (utarray_reserve() calls realloc). If some thread
was iterating the array while another was resizing the array, the first one
would iterate on a freed array, thus accessing invalid memory.

On NuttX this could lead to hardfaults in rare conditions.

Unfortunately we need to initialize the semaphore on startup, by calling
sem_init(). This adds a param_init() method called by every board/config
that uses the params (at least I think I've found all of them)

src/platforms/posix/px4_layer/px4_posix_impl.cpp

@@ -46,7 +46,7 @@
 #include <signal.h>
 #include <errno.h>
 #include <unistd.h>
-#include "systemlib/param/param.h"
+#include <systemlib/param/param.h>
 #include "hrt_work.h"
 #include <drivers/drv_hrt.h>
 #include "px4_time.h"
@@ -76,6 +76,7 @@ void init_once()
 	work_queues_init();
 	hrt_work_queue_init();
 	hrt_init();
+	param_init();
 
 #ifdef CONFIG_SHMEM
 	PX4_DEBUG("Syncing params to shared memory\n");

src/platforms/qurt/px4_layer/px4_qurt_impl.cpp

@@ -48,7 +48,7 @@
 #include <errno.h>
 #include <unistd.h>
 #include <semaphore.h>
-#include "systemlib/param/param.h"
+#include <systemlib/param/param.h>
 #include "hrt_work.h"
 #include "px4_log.h"
 
@@ -106,6 +106,7 @@ void init_once(void)
 	work_queues_init();
 	hrt_work_queue_init();
 	hrt_init();
+	param_init();
 
 	/* Shared memory param sync*/
 	init_params();