In debian/ubuntu, libc.so is located at a different place,
/lib/x86_64-linux-gnu/libc-2.23.so, so it outputs like this when testing:

  PING ::1(::1) 56 data bytes
  64 bytes from ::1: icmp_seq=1 ttl=64 time=0.040 ms

  --- ::1 ping statistics ---
  1 packets transmitted, 1 received, 0% packet loss, time 0ms
  rtt min/avg/max/mdev = 0.040/0.040/0.040/0.000 ms
  0.000 probe_libc:inet_pton:(7f0e2db741c0))
  __GI___inet_pton (/lib/x86_64-linux-gnu/libc-2.23.so)
  getaddrinfo (/lib/x86_64-linux-gnu/libc-2.23.so)
  [0xffffa9d40f34ff4d] (/bin/ping)

Fix up the libc path to make sure this test works in more OSes.

Committer testing:

When this test fails one can use 'perf test -v', i.e. in verbose mode, where
it'll show the expected backtrace, so, after applying this test:

On Fedora 26:

  # perf test -v ping
  62: probe libc's inet_pton & backtrace it with ping       :
  --- start ---
  test child forked, pid 23322
  PING ::1(::1) 56 data bytes
  64 bytes from ::1: icmp_seq=1 ttl=64 time=0.058 ms
  --- ::1 ping statistics ---
  1 packets transmitted, 1 received, 0% packet loss, time 0ms
  rtt min/avg/max/mdev = 0.058/0.058/0.058/0.000 ms
  0.000 probe_libc:inet_pton:(7fe344310d80))
  __GI___inet_pton (/usr/lib64/libc-2.25.so)
  getaddrinfo (/usr/lib64/libc-2.25.so)
  _init (/usr/bin/ping)
  test child finished with 0
  ---- end ----
  probe libc's inet_pton & backtrace it with ping: Ok
  #
Signed-off-by: Li Zhijian <lizhijian@cn.fujitsu.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Kim Phillips <kim.phillips@arm.com>
Cc: Li Zhijian <lizhijian@cn.fujitsu.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Philip Li <philip.li@intel.com>
Link: http://lkml.kernel.org/r/1508315649-18836-1-git-send-email-lizhijian@cn.fujitsu.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>