ip-xfrm: Respect family in deleteall and list commands

ip-xfrm: Respect family in deleteall and list commands

Allow to limit 'ip xfrm {state|policy} list' output to a certain address
family and to delete all states/policies by family.

Although preferred_family was already set in filters, the filter
function ignored it. To enable filtering despite the lack of other
selectors, filter.use has to be set if family is not AF_UNSPEC.

Signed-off-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>