net: ipv4: reset check_lifetime_work after changing lifetime

This will result in calling check_lifetime in nearest opportunity and
that function will adjust next time to call check_lifetime correctly.
Without this, check_lifetime is called in time computed by previous run,
not affecting modified lifetime.

Introduced by: commit 5c766d64

 "ipv4: introduce address lifetime"

Signed-off-by: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: David S. Miller <davem@davemloft.net>