apps.ipv4.arp: add request/reply counters
apps.ipv4.arp: add request/reply counters

Igalia/snabb,eugeneia/snabb,Igalia/snabb,eugeneia/snabb,eugeneia/snabb,eugeneia/snabb,Igalia/snabb,snabbco/snabb,snabbco/snabb,Igalia/snabb,SnabbCo/snabbswitch,SnabbCo/snabbswitch,Igalia/snabb,eugeneia/snabb,Igalia/snabb,snabbco/snabb,snabbco/snabb,eugeneia/snabb,snabbco/snabb,SnabbCo/snabbswitch,eugeneia/snabb,Igalia/snabb,snabbco/snabb,SnabbCo/snabbswitch,Igalia/snabb,snabbco/snabb,eugeneia/snabb,snabbco/snabb