Improve the APF test by changing the packet count assertion from
`== 1` to `> matched_pkt_count_before_test`.
This handles scenarios where the packet counter might already
have a non-zero value or increment due to other traffic, making
the test more reliable. The test now asserts that the specific
test packet caused the counter to increase.
Flag: EXEMPT test only
Bug: 419427388
Test: atest CtsConnectivityMultiDevicesTestCases:ApfV6Test
Change-Id: Id3c0de786e674214948e7030519fe25383c9958c
c4fcf02870