Add gcc-multilib as eBPF pre-requisite for Ubuntu

[jaehnri]

What kind of PR is this?

Documentation

Why this PR is needed / What does this PR do?

I had a little trouble compiling the eBPF program in Ubuntu:

$ make bytecode
...
bpf2go -cc clang -cflags -O2 -g -Wall -Werror -I./libbpf/include -I./libbpf/src bpf ./bpf/cgroup_connect4.c
In file included from /home/joao/Github/kpng/backends/ebpf/bpf/cgroup_connect4.c:3:
In file included from ./libbpf/include/uapi/linux/bpf.h:11:
/usr/include/linux/types.h:5:10: fatal error: 'asm/types.h' file not found
#include <asm/types.h>
         ^~~~~~~~~~~~~
1 error generated.
Error: can't execute clang: exit status 1
ebpf.go:45: running "bpf2go": exit status 1
make: *** [Makefile:24: bytecode] Error 1

Looking for a fix, I found https://github.com/xdp-project/xdp-tools/issues/4, that points to https://github.com/xdp-project/xdp-tutorial/issues/44, which then proceeds to recommend the installation of gcc-multilib.

This extra requirement may save someone else's time futurely.

[jayunit100]

/lgtm /approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: jaehnri, jayunit100

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[aroradaman]

@jaehnri can you look at https://github.com/kubernetes-sigs/kpng/actions/runs/5067777691/jobs/9099251795 the ci is unable to install gcc-multilib and breaking the tests.

[jaehnri]

@aroradaman this is very weird. gcc-multilib has always been an eBPF dependency, this is just a docs change: https://github.com/kubernetes-sigs/kpng/blame/master/.github/workflows/e2e_tests.yaml#L61

I think a sudo apt update will help. Will open it.