airoha: allow selecting 6.1 as test kernel

Add 6.1 as the test kernel for airoha.

Signed-off-by: Robert Marko <[email protected]>

target/linux/airoha/Makefile

@@ -7,6 +7,7 @@ CPU_TYPE:=cortex-a7
 FEATURES:=dt squashfs nand ramdisk gpio source-only
 
 KERNEL_PATCHVER:=5.15
+KERNEL_TESTING_PATCHVER:=6.1
 
 include $(INCLUDE_DIR)/target.mk