pxelinux: with ks/bonding optional/best-effort, do not report an error when ks/bonding is not defined and an invalid bondig device is passed to pxe_network_bonding
pxelinux: with ks/bonding optional/best-effort, do not report an error when ks/bonding is not defined and an invalid bondig device is passed to pxe_network_bonding

quattor/aii,alvarosimon/aii,stdweird/aii,jrha/aii,jrha/aii,stdweird/aii,alvarosimon/aii