IB/ipoib: Fix memory leaks for child interfaces priv

There is a need to free priv explicitly and not just to release
the device, child priv is freed explicitly on remove flow and this
patch also includes priv free on error flow in P_key creation
and also in add_port.

Fixes: cd565b4b ('IB/IPoIB: Support acceleration options callbacks')
Signed-off-by: Alex Vesker <valex@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Doug Ledford <dledford@redhat.com>