routing: cap number of yen's algorithm iterations at 100
routing: cap number of yen's algorithm iterations at 100

This commit makes a precautionary change in order to ensure that the
upper bound on the number of iteration’s within our version of Yen’s
algorithm is fixed.

LightningNetwork/lnd,aakselrod/lnd,LightningNetwork/lnd,ddustin/lnd,ddustin/lnd,aakselrod/lnd