Add network_stack command for capturing and matching packets

For APFv6 multi-devices test, it needs to capture reply packets,
and verify if the packets are expected pattern.

3 new commands are introduced in network_stack:
- cmd network apf <iface> start-capture
- cmd network apf <iface> stop-capture
- cmd network apf <iface> matched-packet-counts <pkt-in-hex>

Test: atest NetworkStackTests
Test: manual
Change-Id: Icc7126de398991f62e2a538678609ee1db442afc
3 files changed