snet: Use correct base conn (#3134)
snet: Use correct base conn (#3134)

This PR makes the reader and writer conn of snet to point to the correct
base conn.

fixes #3133
netsec-ethz/scion,netsec-ethz/scion,Oncilla/scion,Oncilla/scion,netsec-ethz/scion,Oncilla/scion,netsec-ethz/scion,Oncilla/scion