ROMFS: don't check for UAVCAN_ENABLE param in SITL

This prevents a warning message being printed to SITL users because the
UAVCAN_ENABLE param does not exist.

ROMFS/px4fmu_common/init.d/rc.logging

@@ -4,10 +4,13 @@
 # NOTE: Script variables are declared/initialized/unset in the rcS script.
 #
 
-if param greater UAVCAN_ENABLE 1
+if ! ver hwcmp PX4_SITL
 then
-	# Reduce logger buffer to free up some RAM for UAVCAN servers.
-	set LOGGER_BUF 6
+	if param greater UAVCAN_ENABLE 1
+	then
+		# Reduce logger buffer to free up some RAM for UAVCAN servers.
+		set LOGGER_BUF 6
+	fi
 fi
 
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