packet: cast pointer arg in from_pointer()
packet: cast pointer arg in from_pointer()

The pointer type passed to append() and prepend() should always be
canonicalized to "uint8_t *" to avoid side traces in code that uses
these functions.

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