module: use list_add_tail_rcu() when adding module

Put a new module at the end of the list given when we
traverse the list with find_module_all() we look at the
first entry first, if we're loading a series of modules
chances are good what we look for can be in the front of
the list. This is specially true if we somehow end up adding
multiple module entries into the list, the fist one added
should become live first than the ones added last.

Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org>