[dnm/rfc] remove cilium/ebpf dependency to save 1.1M

[kolyshkin]

This replaces use of the main cilium/ebpf package (in oc/cgroups) by our
own code, while keeping the usage of cilium/ebpf/asm.

As a result, runc binary is about 1MB smaller, which is ~7% savings:

[kir@kir-tp1 runc]$ size runc.before runc
   text	   data	    bss	    dec	    hex	filename
6492732	4615697	 229160	11337589	 acff75	runc.before
6018676	4319913	 228392	10566981	 a13d45	runc

[kir@kir-tp1 runc]$ ls -la runc.before runc
-rwxr-xr-x. 1 kir kir 15749568 Apr  2 16:31 runc.before
-rwxr-xr-x. 1 kir kir 14687496 Apr  2 16:31 runc

[kir@kir-tp1 runc]$ gsa runc.before runc
┌─────────────────────────────────────────────────────────────────────────────────┐
│ Diff between runc.before and runc                                               │
├─────────┬───────────────────────────────────────┬──────────┬──────────┬─────────┤
│ PERCENT │ NAME                                  │ OLD SIZE │ NEW SIZE │ DIFF    │
├─────────┼───────────────────────────────────────┼──────────┼──────────┼─────────┤
│ +0.42%  │ github.com/opencontainers/cgroups     │ 323 kB   │ 324 kB   │ +1.4 kB │
│ -3.97%  │ encoding/binary                       │ 55 kB    │ 53 kB    │ -2.2 kB │
│ -8.65%  │ bytes                                 │ 27 kB    │ 25 kB    │ -2.3 kB │
│ -5.31%  │ golang.org/x/sys                      │ 82 kB    │ 78 kB    │ -4.4 kB │
│ -15.93% │ debug/elf                             │ 42 kB    │ 35 kB    │ -6.6 kB │
│ -37.61% │ math                                  │ 24 kB    │ 15 kB    │ -9.2 kB │
│ -9.25%  │ <autogenerated>                       │ 155 kB   │ 141 kB   │ -14 kB  │
│ -83.62% │ github.com/cilium/ebpf                │ 652 kB   │ 107 kB   │ -545 kB │
├─────────┼───────────────────────────────────────┼──────────┼──────────┼─────────┤
│ -10.30% │ .data                                 │ 52 kB    │ 47 kB    │ -5.4 kB │
│ -7.00%  │ .debug_frame                          │ 159 kB   │ 148 kB   │ -11 kB  │
│ -6.05%  │ .debug_ranges                         │ 254 kB   │ 239 kB   │ -15 kB  │
│ -6.14%  │ .symtab                               │ 419 kB   │ 393 kB   │ -26 kB  │
│ -6.61%  │ .rodata                               │ 675 kB   │ 631 kB   │ -45 kB  │
│ -6.39%  │ .debug_line                           │ 739 kB   │ 692 kB   │ -47 kB  │
│ -6.70%  │ .strtab                               │ 762 kB   │ 711 kB   │ -51 kB  │
│ -8.93%  │ .data.rel.ro                          │ 680 kB   │ 620 kB   │ -61 kB  │
│ -7.35%  │ .debug_loc                            │ 840 kB   │ 778 kB   │ -62 kB  │
│ -5.87%  │ .debug_info                           │ 1.4 MB   │ 1.4 MB   │ -85 kB  │
│ -7.62%  │ .rela.dyn                             │ 1.1 MB   │ 1.1 MB   │ -87 kB  │
├─────────┼───────────────────────────────────────┼──────────┼──────────┼─────────┤
│ -6.74%  │ runc.before                           │ 16 MB    │ 15 MB    │ -1.1 MB │
│         │ runc                                  │          │          │         │
└─────────┴───────────────────────────────────────┴──────────┴──────────┴─────────┘

I am unsure if the added maintenance cost is worth the savings, so this is more like an experiment and a request for comments.

[kolyshkin]

A quick observation (which is semi-relevant to this PR). The runc binary used to be 12M only a few years ago (see #3460 (comment)), and it's 15-16M now.

I guess the biggest issue here is we're using packages that eventually grow in size (due to feature creep etc), which is not a problem per se, but becomes a problem together with disabled DCE, and DCE is disabled due to use of introspection/reflect in some of our dependencies. So, we are bundling some code into our binary which is never used. To re-enable DCE we need to eliminate the use of reflect.Method etc.