list: introduce list_first_entry_or_null

non-rcu variant of list_first_or_null_rcu

Change-Id: Ibc8b476ef382e93c659d14a27364c896f81bd689
Signed-off-by: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: MassStash <MassStash@gmail.com>