bpf: Remove redundant ifdef

Remove a useless ifdef __NR_bpf as requested by Wang Nan.

Inline one-line static functions as it was in the bpf_sys.h file.

Signed-off-by: Mickaël Salaün <mic@digikod.net>
Cc: Alexei Starovoitov <ast@fb.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: David S. Miller <davem@davemloft.net>
Cc: Wang Nan <wangnan0@huawei.com>
Link: https://lkml.kernel.org/r/828ab1ff-4dcf-53ff-c97b-074adb895006@huawei.com
Acked-by: Wang Nan <wangnan0@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>