bpf: Bloom filter map naming fixups

This patch has two changes in the kernel bloom filter map
implementation:

1) Change the names of map-ops functions to include the
"bloom_map" prefix.

As Martin pointed out on a previous patchset, having generic
map-ops names may be confusing in tracing and in perf-report.

2) Drop the "& 0xF" when getting nr_hash_funcs, since we
already ascertain that no other bits in map_extra beyond the
first 4 bits can be set.

Signed-off-by: Joanne Koong <joannekoong@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20211029224909.1721024-2-joannekoong@fb.com