Introduce APF shell command to dump counters
Adds a new APF shell command: `cmd network_stack apf <iface> counters`.
This command allows users to dump relavant APF counters for testing purpose.
The output format for the counters will be displayed as follows:
```
$ adb shell cmd network_stack apf wlan0 counters
ENDIANNESS: 305419896
TOTAL_PACKETS: 429
FILTER_AGE_SECONDS: 141
FILTER_AGE_16384THS: 2318517
APF_VERSION: 6000
APF_PROGRAM_ID: 10
PASSED_ARP_UNICAST_REPLY: 3
PASSED_DHCP: 1
PASSED_IPV4_UNICAST: 157
PASSED_IPV6_ICMP: 3
PASSED_IPV6_UNICAST_NON_ICMP: 209
PASSED_RA: 1
DROPPED_IPV4_BROADCAST_ADDR: 3
DROPPED_IPV4_BROADCAST_NET: 31
DROPPED_IPV4_MULTICAST: 1
DROPPED_IPV6_NS_OTHER_HOST: 3
DROPPED_IPV6_NS_REPLIED_NON_DAD: 4
DROPPED_ETHERTYPE_NOT_ALLOWED: 4
DROPPED_ARP_OTHER_HOST: 5
DROPPED_ARP_REQUEST_REPLIED: 4
```
Flag: EXEMPT mainline
Bug: 419423721
Test: flahs device and check `adb shell cmd network_stack apf wlan0 counters`
Change-Id: I816951628f3035a35e1ff9519ba8dbbdb2af7cdb
2 files changed
