Add define for SSP (multipath stream socket)
Add define for SSP (multipath stream socket)

It might be possible to share the protocol number with SDAMP, need to
think about it some more

netsec-ethz/scion,FR4NK-W/osourced-scion,FR4NK-W/osourced-scion,netsec-ethz/scion,dmpiergiacomo/scion,dmpiergiacomo/scion,Oncilla/scion,dmpiergiacomo/scion,klausman/scion,dmpiergiacomo/scion,Oncilla/scion,klausman/scion,dmpiergiacomo/scion,klausman/scion,netsec-ethz/scion,FR4NK-W/osourced-scion,FR4NK-W/osourced-scion,Oncilla/scion,FR4NK-W/osourced-scion,netsec-ethz/scion,klausman/scion,dmpiergiacomo/scion,klausman/scion,Oncilla/scion