Save the alignment hints and reuse them in each ncmpi__enddef

[wkliao]

ncmpi_endf and ncmpi__enddef may be called multiple times. We need to save the alignment hints, h_align, v_align, and r_align as they maybe changed in each call to ncmpienddef. Reset them to the original hints allows users to use different alignments in each call to ncmpienddef.