include: linux: Update kernel.h

include: linux: Update kernel.h

Its contents were moved into const.h and sysinfo.h, apply these changes
to the cached copies. Fixes for the following warning when compiling
xtables-monitor.c with new kernel headers in /usr/include:

| In file included from ../include/linux/netfilter/x_tables.h:3,
|                  from ../include/xtables.h:19,
|                  from xtables-monitor.c:36:
| ../include/linux/kernel.h:7: warning: "__ALIGN_KERNEL" redefined
|     7 | #define __ALIGN_KERNEL(x, a)            __ALIGN_KERNEL_MASK(x, (typeof(x))(a) - 1)
|       |
| In file included from /usr/include/linux/netlink.h:5,
|                  from /home/n0-1/git/libmnl/install/include/libmnl/libmnl.h:9,
|                  from xtables-monitor.c:30:
| /usr/include/linux/const.h:31: note: this is the location of the previous definition
|    31 | #define __ALIGN_KERNEL(x, a)            __ALIGN_KERNEL_MASK(x, (__typeof__(x))(a) - 1)
|       |

Signed-off-by: Phil Sutter <phil@nwl.cc>