libxl: memory size in kb requires 64 bit variable

libxl: memory size in kb requires 64 bit variable

libxl_set_memory_target() and several other interface functions of
libxl use a 32 bit sized parameter for a memory size value in kBytes.
This limits the maximum size to be passed in such a parameter
depending on signedness of the parameter to 2TB or 4TB.

Correct this by using 64 bit types.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Dario Faggioli <dario.faggioli@citrix.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>