perf tests: Fix record+probe_libc_inet_pton.sh for powerpc64

perf tests: Fix record+probe_libc_inet_pton.sh for powerpc64

'probe libc's inet_pton & backtrace it with ping' testcase sometimes
fails on powerpc because distro ping binary does not have symbol
information and thus it prints "[unknown]" function name in the
backtrace.

Accept "[unknown]" as valid function name for powerpc as well.

 # perf test -v "probe libc's inet_pton & backtrace it with ping"

Before:

  59: probe libc's inet_pton & backtrace it with ping       :
  --- start ---
  test child forked, pid 79695
  ping 79718 [077] 96483.787025: probe_libc:inet_pton: (7fff83a754c8)
  7fff83a754c8 __GI___inet_pton+0x8 (/usr/lib64/power9/libc-2.28.so)
  7fff83a2b7a0 gaih_inet.constprop.7+0x1020
  (/usr/lib64/power9/libc-2.28.so)
  7fff83a2c170 getaddrinfo+0x160 (/usr/lib64/power9/libc-2.28.so)
  1171830f4 [unknown] (/usr/bin/ping)
  FAIL: expected backtrace entry
  ".*\+0x[[:xdigit:]]+[[:space:]]\(.*/bin/ping.*\)$"
  got "1171830f4 [unknown] (/usr/bin/ping)"
  test child finished with -1
  ---- end ----
  probe libc's inet_pton & backtrace it with ping: FAILED!

After:

  59: probe libc's inet_pton & backtrace it with ping       :
  --- start ---
  test child forked, pid 79085
  ping 79108 [045] 96400.214177: probe_libc:inet_pton: (7fffbb9654c8)
  7fffbb9654c8 __GI___inet_pton+0x8 (/usr/lib64/power9/libc-2.28.so)
  7fffbb91b7a0 gaih_inet.constprop.7+0x1020
  (/usr/lib64/power9/libc-2.28.so)
  7fffbb91c170 getaddrinfo+0x160 (/usr/lib64/power9/libc-2.28.so)
  132e830f4 [unknown] (/usr/bin/ping)
  test child finished with 0
  ---- end ----
  probe libc's inet_pton & backtrace it with ping: Ok

Signed-off-by: Seeteena Thoufeek <s1seetee@linux.vnet.ibm.com>
Reviewed-by: Kim Phillips <kim.phillips@amd.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Hendrik Brueckner <brueckner@linux.ibm.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Michael Petlan <mpetlan@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sandipan Das <sandipan@linux.ibm.com>
Fixes: 1632936480a5 ("perf tests: Fix record+probe_libc_inet_pton.sh without ping's debuginfo")
Link: http://lkml.kernel.org/r/1561630614-3216-1-git-send-email-s1seetee@linux.vnet.ibm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>