DNM: Batch APIS reproducer

[msherif1234]

Using custom k and v to reproduce performance issues with BatchLookupAndDelete apis for perCPUHashmap

marshallers seems to have an issue if the fields of the key of different type ? u will get an error like e"[]ebpf.customKey doesn't marshal to 1600 bytes" aas an example if u have u32 and u64 fields in the key or value structures

 go test . -exec sudo -bench=BenchmarkCustomIterate  -benchmem -count 5 -run=^#
goos: linux
goarch: amd64
pkg: github.com/cilium/ebpf
cpu: Intel(R) Core(TM) i7-10850H CPU @ 2.70GHz
BenchmarkCustomIterate/PerCPUHash/MapIteratorDelete-12         	    3397	    349858 ns/op	   40982 B/op	     304 allocs/op
BenchmarkCustomIterate/PerCPUHash/MapIteratorDelete-12         	    3410	    359623 ns/op	   40982 B/op	     304 allocs/op
BenchmarkCustomIterate/PerCPUHash/MapIteratorDelete-12         	    3447	    354813 ns/op	   40982 B/op	     304 allocs/op
BenchmarkCustomIterate/PerCPUHash/MapIteratorDelete-12         	    3302	    351545 ns/op	   40983 B/op	     304 allocs/op
BenchmarkCustomIterate/PerCPUHash/MapIteratorDelete-12         	    3481	    351126 ns/op	   40982 B/op	     304 allocs/op
BenchmarkCustomIterate/PerCPUHash/BatchLookupAndDelete-12      	    6835	    174716 ns/op	   22960 B/op	     106 allocs/op
BenchmarkCustomIterate/PerCPUHash/BatchLookupAndDelete-12      	    6793	    177632 ns/op	   22960 B/op	     106 allocs/op
BenchmarkCustomIterate/PerCPUHash/BatchLookupAndDelete-12      	    6626	    177139 ns/op	   22960 B/op	     106 allocs/op
BenchmarkCustomIterate/PerCPUHash/BatchLookupAndDelete-12      	    7083	    170590 ns/op	   22960 B/op	     106 allocs/op
BenchmarkCustomIterate/PerCPUHash/BatchLookupAndDelete-12      	    6824	    169559 ns/op	   22960 B/op	     106 allocs/op
PASS
ok  	github.com/cilium/ebpf	35.080s