Fix kexec_unload failure on secure boot enabled platforms

[vivekrnv]

Why I did

kexec -u on systems with SB enabled is failing

root@sn5600:/home/admin# mokutil --sb-state
SecureBoot enabled
root@sn5600:/home/admin# kexec -u
kexec unload failed: Permission denied

[ 3443.199576] ima: impossible to appraise a kernel image without a file descriptor; try using kexec_file_load syscall.

How I did it

How to verify it

Use the -a argument with kexec

 -a, --kexec-syscall-auto  Use file based syscall for kexec and fall
                      back to the compatibility syscall when file based
                      syscall is not supported or the kernel did not
                      understand the image

Previous command output (if the output of a command-line utility has changed)

New command output (if the output of a command-line utility has changed)

[vivekrnv]

@davidpil2002 please review

[davidpil2002]

we use this flag when calling this function
function load_kernel() {
# Load kernel into the memory
invoke_kexec -a
}
do this solution to unload looks good to me as well

[davidpil2002]

see my comment in notes