kernel: bump 6.6 to 6.6.38

kernel: bump 6.6 to 6.6.38

Changelog: https://cdn.kernel.org/pub/linux/kernel/v6.x/ChangeLog-6.6.38

Removed target/linux/generic/hack-6.6/900-fix-build-to-handle-return-value.patch
which was introduced as a hacky attempt to fix an upstream issue related to 6.6.37.

Build system: x86/64
Build-tested: x86/64/AMD Cezanne, flogic/xiaomi_redmi-router-ax6000-ubootmod, ramips/tplink_archer-a6-v3
Run-tested: x86/64/AMD Cezanne, flogic/xiaomi_redmi-router-ax6000-ubootmod, ramips/tplink_archer-a6-v3

Signed-off-by: John Audia <therealgraysky@proton.me>
Link: https://github.com/openwrt/openwrt/pull/15879
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>