dm mpath: make pg_init_delay_msecs settable

"pg_init_delay_msecs X" can be passed as a feature in the multipath
table and is used to set m->pg_init_delay_msecs in parse_features().
However, alloc_multipath_stage2(), which is called after
parse_features(), resets m->pg_init_delay_msecs to its default value.
Instead, set m->pg_init_delay_msecs in alloc_multipath(), which is
called before parse_features(), to avoid overwriting a value passed in
by the table.

Signed-off-by: Benjamin Marzinski <bmarzins@redhat.com>
Cc: stable@vger.kernel.org