tools/bpf: print out btf log at LIBBPF_WARN level

Currently, the btf log is allocated and printed out in case
of error at LIBBPF_DEBUG level.
Such logs from kernel are very important for debugging.
For example, bpf syscall BPF_PROG_LOAD command can get
verifier logs back to user space. In function load_program()
of libbpf.c, the log buffer is allocated unconditionally
and printed out at pr_warning() level.

Let us do the similar thing here for btf. Allocate buffer
unconditionally and print out error logs at pr_warning() level.
This can reduce one global function and
optimize for common situations where pr_warning()
is activated either by default or by user supplied
debug output function.

Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

tools/lib/bpf/libbpf.c

@@ -98,16 +98,6 @@ void libbpf_print(enum libbpf_print_level level, const char *format, ...)
 	va_end(args);
 }
 
-bool libbpf_print_level_available(enum libbpf_print_level level)
-{
-	if (level == LIBBPF_WARN)
-		return !!__pr_warning;
-	else if (level == LIBBPF_INFO)
-		return !!__pr_info;
-	else
-		return !!__pr_debug;
-}
-
 #define STRERR_BUFSIZE  128
 
 #define CHECK_ERR(action, err, out) do {	\