Add BatchLookup support for a pointer to a slice

BatchLookup claims it doesn't support a pointer to a slice, but sysenc.SyscallOutput does support pointers to slices: https://github.com/cilium/ebpf/blob/99a4e69ca83e4a01c3600e9d4c91d856b12531c0/internal/sysenc/marshal.go#L144-L146

Could batchCount and sliceLen be updated to support pointer to slices?