pf tests: check cleared time when zeroing stats for table addresses
    
    Verify that we reset the cleared time when we zero an address' counters in
    a table.
    
    PR:		282877, 282984
    Reviewed by:	kp
    MFC after:	2 weeks
    Signed-off-by:	Leonid Evdokimov <leon@darkk.net.ru>
    Differential Revision:	https://reviews.freebsd.org/D48242
    
    (cherry picked from commit 0749d8134300b8e3c956e161890ab496247d2542)