pkg/ipcache: cache prefix.String() in allocateCIDRs
pkg/ipcache: cache prefix.String() in allocateCIDRs

To avoid calculating String() of the given prefix we can calculate it
once and re-use the calculated value in the function.

Signed-off-by: André Martins <bc9800b9d52a24cce72a73dd528afed53f10e5fc@cilium.io>

cilium-team/cilium,michi-covalent/cilium,tgraf/cilium,tklauser/cilium,michi-covalent/cilium,michi-covalent/cilium,tgraf/cilium,tgraf/cilium,tgraf/cilium,tklauser/cilium,cilium/cilium,michi-covalent/cilium,cilium/cilium,cilium/cilium,tklauser/cilium,cilium-team/cilium,michi-covalent/cilium,tgraf/cilium,cilium/cilium,cilium/cilium,tklauser/cilium,tklauser/cilium,tgraf/cilium