lib.protocol.ethernet: fix truncation bug in ptoi
lib.protocol.ethernet: fix truncation bug in ptoi

bit munging was broken because of truncation to u8

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