[dm-devel] nit with reinstate_path for dm-mpath.c

[goggin, edward]

Should reinstate_path() in dm-mpath.c only conditionally reset
current_pgpath if
the restored path is in the same path priority group as the current_pgpath
instead
of doing so unconditionally as is done currently?  Albeit this change makes
sense
IFF it is architecturally invalid to have a path selection policy which
spans multiple
path priority groups -- as I think is currently the case.