perf tests: Fix record+probe_libc_inet_pton.sh without ping's debuginfo

perf tests: Fix record+probe_libc_inet_pton.sh without ping's debuginfo

When we don't have the iputils-debuginfo package installed, i.e. when we
don't have the DWARF information needed to resolve ping's samples, we
end up failing this 'perf test' entry:

  # perf test ping
  62: probe libc's inet_pton & backtrace it with ping       : Ok
  # rpm -e iputils-debuginfo
  # perf test ping
  62: probe libc's inet_pton & backtrace it with ping       : FAILED!
  #

Fix it to accept "[unknown]" where the symbol + offset, when resolved,
is expected.

I think this will fail in the other arches as well, but since I can't
test now, I'm leaving s390x and ppc cases as-is.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kim Phillips <kim.phillips@arm.com>
Cc: Michael Petlan <mpetlan@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Cc: Sandipan Das <sandipan@linux.vnet.ibm.com>
Cc: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Cc: Thomas Richter <tmricht@linux.vnet.ibm.com>
Cc: Wang Nan <wangnan0@huawei.com>
Fixes: 7903a7086723 ("perf script: Show symbol offsets by default")
Link: https://lkml.kernel.org/n/tip-hnizqwqrs03vcq1b74yao0f6@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>