* Linux: Update kernel 5.15.25
Use highest available kernel version in Buildroot 2021.08 (5.13)
* Update Hardkernel patches to Linux 5.15
* Update generic-x86-64/ova kernel config/patches for 5.15
* Drop Intel e1000e Sourceforge driver
The driver has been discontinued sometime last year. The main reason the
out-of-tree kernel has been enabled was for support for the i219-V
network chips which meanwhile are supported in mainline.
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