5429411f73
In light of https://github.com/openwrt/openwrt/issues/11077, switch mvebu
to 5.15 which has been the testing kernel on this target since April - over
half a year.
Run-tested on the following subtargets:
* cortexa9 (Turris Omnia - 03f41b1eb2)
* cortexa72 (MikroTik RB5009UG+S+IN)
Tested-by: Enrico Mioso <mrkiko.rs@gmail.com> [GL-MV1000]
Signed-off-by: Stijn Segers <foss@volatilesystems.org>