crashkernel/mxgrub: enable crashkernel only on servers

Size limiting (64G-:256M) is explained in the kernel docs
  -> admin-guide/kdump/kdump.rst (Extended crashkernel syntax)

The memory occupied can be checked with:

  #> cat /sys/kernel/kexec_crash_size

mxgrub/mxgrub

@@ -240,7 +240,7 @@ sub scan_mariux {
 	}
 }
 
-our $KERNEL_PARAMETER="ro crashkernel=256M console=ttyS0,115200n8 console=tty0 init=/bin/systemd audit=0 random.trust_cpu=on";
+our $KERNEL_PARAMETER="ro crashkernel=64G-:256M console=ttyS0,115200n8 console=tty0 init=/bin/systemd audit=0 random.trust_cpu=on";
 
 sub update_grub_cfg {
 	my $kernellist='';