sros: refactor bootstrap spin
sros: refactor bootstrap spin

Some needed simplification. This is inline with changes previously done
for vMX.

holmahenkel/vrnetlab,plajjan/vrnetlab,bdreisbach/vrnetlab,bdreisbach/vrnetlab,mzagozen/vrnetlab,mzagozen/vrnetlab,plajjan/vrnetlab,holmahenkel/vrnetlab