labels/cidr: add BenchmarkIPStringToLabel
labels/cidr: add BenchmarkIPStringToLabel

These allow to establish a base line for future performance
improvements:

    BenchmarkIPStringToLabel/0.0.0.0/0-8         	 2217088	       542.3 ns/op	      96 B/op	       6 allocs/op
    BenchmarkIPStringToLabel/192.0.2.3-8         	 2415202	       502.4 ns/op	      88 B/op	       5 allocs/op
    BenchmarkIPStringToLabel/192.0.2.3/32-8      	 2161540	       552.3 ns/op	     109 B/op	       6 allocs/op
    BenchmarkIPStringToLabel/192.0.2.3/24-8      	 2051430	       537.1 ns/op	     109 B/op	       6 allocs/op
    BenchmarkIPStringToLabel/192.0.2.0/24-8      	 2135937	       560.4 ns/op	     109 B/op	       6 allocs/op
    BenchmarkIPStringToLabel/::/0-8              	 1850794	       661.8 ns/op	     112 B/op	       7 allocs/op
    BenchmarkIPStringToLabel/fdff::ff-8          	 1460982	       849.0 ns/op	     136 B/op	       8 allocs/op
    BenchmarkIPStringToLabel/f00d:42::ff/128-8   	 1105088	      1033 ns/op	     200 B/op	       9 allocs/op
    BenchmarkIPStringToLabel/f00d:42::ff/96-8    	 1381957	       895.8 ns/op	     152 B/op	       7 allocs/op

Also extend TestIPStringToLabel to cover some more IPv6 CIDR formats.

Signed-off-by: Tobias Klauser <059b8b880f8441509ec8a65b50b4c6ae74ebea76@cilium.io>

cilium/cilium,cilium/cilium,michi-covalent/cilium,michi-covalent/cilium,cilium/cilium,cilium/cilium,michi-covalent/cilium,cilium/cilium,michi-covalent/cilium,michi-covalent/cilium