ecl: Update ekf2 to version that addresses known vulnerabilities

See:

https://github.com/PX4/ecl/pull/350
https://github.com/PX4/ecl/pull/354

Note the amount of stack allocation has had to be increased to accomodate pr350

src/lib/ecl

@@ -1 +1 @@
-Subproject commit f921b2de5cbcf309cdf61c2cbe15c0b4dd2ce9b5
+Subproject commit cc651ac4729b339c1187c0e2d7aa03a2943eadf9

src/modules/ekf2/ekf2_main.cpp

@@ -1436,7 +1436,7 @@ int Ekf2::task_spawn(int argc, char *argv[])
 	_task_id = px4_task_spawn_cmd("ekf2",
 				      SCHED_DEFAULT,
 				      SCHED_PRIORITY_ESTIMATOR,
-				      5720,
+				      6600,
 				      (px4_main_t)&run_trampoline,
 				      (char *const *)argv);