bcm4908: switch to Kernel 5.15 by default

Getting ready for the next release.

Signed-off-by: Paul Spooren <[email protected]>
[rmilecki: tested on GT-AC5300: boot, sysupgrade & 940 Mbps NAT]
Signed-off-by: Rafał Miłecki <[email protected]>

target/linux/bcm4908/Makefile

@@ -9,8 +9,7 @@ FEATURES:=squashfs nand usb gpio
 CPU_TYPE:=cortex-a53
 SUBTARGETS:=generic
 
-KERNEL_PATCHVER:=5.10
-KERNEL_TESTING_PATCHVER:=5.15
+KERNEL_PATCHVER:=5.15
 
 define Target/Description
 	Build firmware images for Broadcom BCM4908 SoC family routers.