ns-wrappers: ns-del-if tries to delete two interfaces from the same namespace

The wrapper ns-del-if takes only two arguments : NAME and NAMESPACE when it should take two like the ns-add-if wrapper.

The interfaces created by ns-add-if with the arguments NAME NS1 NS2 are :

${NAME}-1-${NS1}
${NAME}-2-${NS2}

While the wrapper ns-del-if takes only the arguments NAME and NS, and tries to delete the interfaces :

${NAME}-1-${NS}
${NAME}-2-${NS}