rampis: mt7621: resize Edgerouter-X kernel size to 6MB

With the updated partition layout set in dts, set the KERNEL_SIZE
parameter to 6MB allowing builds of Linux 6.1 and later to fit.

Signed-off-by: Tim Lunn <[email protected]>
Tested-by: Mauri Sandberg <[email protected]>
Link: https://github.com/openwrt/openwrt/pull/15194
Signed-off-by: Petr Štetiar <[email protected]>

target/linux/ramips/image/mt7621.mk

@@ -2860,7 +2860,7 @@ define Device/ubnt_edgerouter_common
   DEVICE_VENDOR := Ubiquiti
   IMAGE_SIZE := 256768k
   FILESYSTEMS := squashfs
-  KERNEL_SIZE := 3145728
+  KERNEL_SIZE := 6144k
   KERNEL_INITRAMFS := $$(KERNEL) | \
 	ubnt-erx-factory-image $(KDIR)/tmp/$$(KERNEL_INITRAMFS_PREFIX)-factory.tar
   IMAGE/sysupgrade.bin := sysupgrade-tar | append-metadata