bpftool: Use appropriate permissions for map access

Modify several functions in tools/bpf/bpftool/common.c to allow
specification of requested access for file descriptors, such as
read-only access.

Update bpftool to request only read access for maps when write
access is not required. This fixes errors when reading from maps
that are protected from modification via security_bpf_map.

Signed-off-by: Slava Imameev <slava.imameev@crowdstrike.com>
Reviewed-by: Quentin Monnet <qmo@kernel.org>
Link: https://lore.kernel.org/r/20250620151812.13952-1-slava.imameev@crowdstrike.com


Signed-off-by: Alexei Starovoitov <ast@kernel.org>