tools lib bpf: Fix up FEATURE_{TESTS,DISPLAY} usage

When libbpf was introduced it wrongly asked for the "libelf" and "bpf"
feature tests to be performed (via FEATURE_TESTS), while asking that
"libbpf", "libelf-mmap", "libelf-getphdrnum" and "bpf" to have the
result of its respective tests to be displayed (via FEATURE_DISPLAY).

Due to another recently bug fixed in the tools/build/ infrastructure
("tools build: Fixup feature detection display function name") the
results for the entries in the FEATURE_DISPLAY, for this case, were
appearing as all succeeding, when two of them (the ones only on the
DISPLAY) were not even being performed.

Before:

  $ make -C tools/lib/bpf/
  make: Entering directory '/home/git/linux/tools/lib/bpf'
  Auto-detecting system features:
  ...                        libelf: [ on  ]
  ...             libelf-getphdrnum: [ OFF ]
  ...                   libelf-mmap: [ OFF ]
  ...                           bpf: [ on  ]
  <SNIP>

After, with FEATURE_TESTS == FEATURE_DISPLAY:

  Auto-detecting system features:
  ...                        libelf: [ on  ]
  ...             libelf-getphdrnum: [ on  ]
  ...                   libelf-mmap: [ on  ]
  ...                           bpf: [ on  ]
  <SNIP>

I just inverted, so that it tests the four features but displays just
the libelf and mmap ones, to make it more compact. So it becomes:

  $ make -C tools/lib/bpf/
  make: Entering directory '/home/git/linux/tools/lib/bpf'

  Auto-detecting system features:
  ...                        libelf: [ on  ]
  ...                           bpf: [ on  ]

Acked-by: Jiri Olsa <[email protected]>
Cc: Adrian Hunter <[email protected]>
Cc: Alexei Starovoitov <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: David Ahern <[email protected]>
Cc: Frederic Weisbecker <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Stephane Eranian <[email protected]>
Cc: Wang Nan <[email protected]>
Cc: [email protected]
Fixes: 1b76c13e4b ("bpf tools: Introduce 'bpf' library and add bpf feature check")
Link: http://lkml.kernel.org/n/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

tools/lib/bpf/Makefile

@@ -64,8 +64,8 @@ srctree := $(patsubst %/,%,$(dir $(srctree)))
 #$(info Determined 'srctree' to be $(srctree))
 endif
 
-FEATURE_DISPLAY = libelf libelf-getphdrnum libelf-mmap bpf
-FEATURE_TESTS = libelf bpf
+FEATURE_TESTS = libelf libelf-getphdrnum libelf-mmap bpf
+FEATURE_DISPLAY = libelf bpf
 
 INCLUDES = -I. -I$(srctree)/tools/include -I$(srctree)/arch/$(ARCH)/include/uapi -I$(srctree)/include/uapi
 FEATURE_CHECK_CFLAGS-bpf = $(INCLUDES)