ionic: use lif ident for filter count

Use the lif's ident information for the uc and mc filter
counts rather than the ionic's version, to be sure
we're getting the info that is specific to this lif.

While we're thinking about it, add some missing error
checking where we get the lif's identity information.

Signed-off-by: Shannon Nelson <snelson@pensando.io>
Signed-off-by: David S. Miller <davem@davemloft.net>