kernel: bump 5.15 to 5.15.168

Manually adapted:
   bcm27xx/patches-5.15/950-0166-xhci-Use-more-event-ring-segment-table-entries.patch
     I replaced it with the version from main branch which applies more easily
   bcm27xx/patches-5.15/950-0600-xhci-quirks-add-link-TRB-quirk-for-VL805.patch
   bcm27xx/patches-5.15/950-0605-xhci-refactor-out-TRBS_PER_SEGMENT-define-in-runtime.patch
   bcm27xx/patches-5.15/950-0606-usb-xhci-add-VLI_TRB_CACHE_BUG-quirk.patch
   bcm27xx/patches-5.15/950-0717-usb-xhci-add-a-quirk-for-Superspeed-bulk-OUT-transfe.patch
   bcm53xx/patches-5.15/180-usb-xhci-add-support-for-performing-fake-doorbell.patch
   generic/hack-5.15/645-netfilter-connmark-introduce-set-dscpmark.patch

Added patch:
   generic/backport-5.15/777-netfilter-xtables-fix-typo-causing-some-targets-to-not-load-on-IPv6.patch
      This fixes a bug intoduced in this version.

Adapt kernel configuration for newly added option
CONFIG_PROC_MEM_ALWAYS_FORCE.

Link: https://github.com/openwrt/openwrt/pull/16882
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>

target/linux/ath79/patches-5.15/910-unaligned_access_hacks.patch

@@ -751,7 +751,7 @@ SVN-Revision: 35130
  EXPORT_SYMBOL(xfrm_parse_spi);
 --- a/net/ipv4/tcp_input.c
 +++ b/net/ipv4/tcp_input.c
-@@ -4201,14 +4201,16 @@ static bool tcp_parse_aligned_timestamp(
+@@ -4228,14 +4228,16 @@ static bool tcp_parse_aligned_timestamp(
  {
  	const __be32 *ptr = (const __be32 *)(th + 1);