realtek: add Linux Kernel 5.15 as testing version

realtek: add Linux Kernel 5.15 as testing version

Add Linux Kernel 5.15 support for testing.

Signed-off-by: INAGAKI Hiroshi <[email protected]>
[APRESIA ApresiaLightGS120GT-SS, Panasonic Switch-M24eG PN28240K, Switch-M48eG PN28480K]
Tested-by: INAGAKI Hiroshi <[email protected]>
TP-Link TL-SG2008P
Tested-by: Alexandru Gagniuc <[email protected]>
[D-Link DGS-1210-20, DGS-1210-52, Zyxel XGS1010-12]
Tested-by: Markus Stockhausen <[email protected]>
[Zyxel XGS1250-12]
Tested-by: Lucian Cristian <[email protected]> # Zyxel
[HPE 1920-8G, 1920-48G]
Tested-by: Jan Hoffmann <[email protected]>