Add in the critical nesting save and restore.

Source/portable/IAR/ATMega323/portmacro.s90

@@ -45,6 +45,7 @@ EXTERN SIG_UART_DATA
 EXTERN vTaskSwitchContext
 EXTERN pxCurrentTCB
 EXTERN vTaskIncrementTick
+EXTERN uxCriticalNesting
 
 ; Functions implemented in this file
 ; ----------------------------------
@@ -140,6 +141,8 @@ portSAVE_CONTEXT MACRO
 	st	-y, r27
 	st	-y, r30
 	st	-y, r31
+	lds r0, uxCriticalNesting
+	st	-y, r0					; Store the critical nesting counter.
 
 	lds	r26, pxCurrentTCB		; Finally save the software stack pointer (Y ...
 	lds	r27, pxCurrentTCB + 1	; ... register) into the TCB.
@@ -155,6 +158,8 @@ portRESTORE_CONTEXT MACRO
 	ld	r28, x+					; the TCB into the software stack pointer (...
 	ld	r29, x+					; ... the Y register).
 
+	ld	r0, y+
+	sts	uxCriticalNesting, r0
 	ld	r31, y+					; Restore the registers down to R0.  The Y
 	ld	r30, y+					; register is missing from this list as it
 	ld	r27, y+					; has already been restored.