Warn about non-supported flags in map specs

[aditighag]

When an LRU map spec has the BPF_F_NO_PREALLOC flag, the library fails to load BPF programs with the error - map create: operation not supported (without BTF k/v). This is misleading, as the main issue here is that the kernel doesn't support these flags for LRU type maps.

The library could give hints about such not supported configurations while loading map specs.

It could be a candidate for good first issues, but I'll leave the judgement call to you. /cc @ti-mo

[kwakubiney]

Looks like something I'd like to pick up after I wrap this up since it's a similar problem

[kwakubiney]

Same misleading error is seen when noPrealloc flag is used with maps of type BPF_MAP_TYPE_BLOOM_FILTER , BPF_MAP_TYPE_ARRAY , BPF_MAP_TYPE_ARRAY_OF_MAPS , BPF_MAP_TYPE_PERCPU_ARRAY and BPF_MAP_TYPE_RINGBUF. Doesn't look like the library supports BPF_MAP_TYPE_BLOOM_FILTER though