Improve cutoff handling: node connectivity is bounded by minimum degree.
Improve cutoff handling: node connectivity is bounded by minimum degree.

This change imporves significantly the speed of node_connectivity in
denser graphs. For very sparse ones increases speed by ~5%.

ionanrozenfeld/networkx,jakevdp/networkx,blublud/networkx,kernc/networkx,dhimmel/networkx,JamesClough/networkx,dmoliveira/networkx,ionanrozenfeld/networkx,andnovar/networkx,bzero/networkx,chrisnatali/networkx,ionanrozenfeld/networkx,bzero/networkx,sharifulgeo/networkx,bzero/networkx,RMKD/networkx,wasade/networkx,tmilicic/networkx,jni/networkx,debsankha/networkx,jni/networkx,ltiao/networkx,jakevdp/networkx,OrkoHunter/networkx,yashu-seth/networkx,ghdk/networkx,chrisnatali/networkx,jfinkels/networkx,beni55/networkx,kernc/networkx,harlowja/networkx,dhimmel/networkx,nathania/networkx,farhaanbukhsh/networkx,aureooms/networkx,michaelpacer/networkx,aureooms/networkx,jni/networkx,RMKD/networkx,harlowja/networkx,ghdk/networkx,debsankha/networkx,Sixshaman/networkx,farhaanbukhsh/networkx,NvanAdrichem/networkx,aureooms/networkx,jcurbelo/networkx,farhaanbukhsh/networkx,blublud/networkx,sharifulgeo/networkx,nathania/networkx,SanketDG/networkx,sharifulgeo/networkx,nathania/networkx,cmtm/networkx,kernc/networkx,jakevdp/networkx,harlowja/networkx,goulu/networkx,blublud/networkx,dmoliveira/networkx,chrisnatali/networkx,RMKD/networkx,dhimmel/networkx,ghdk/networkx,debsankha/networkx,dmoliveira/networkx