perf callchain: Fix attr.sample_max_stack setting

perf callchain: Fix attr.sample_max_stack setting

When setting the "dwarf" unwinder for a specific event and not
specifying the max-stack, the attr.sample_max_stack ended up using an
uninitialized callchain_param.max_stack, fix it by using designated
initializers for that callchain_param variable, zeroing all non
explicitely initialized struct members.

Here is what happened:

  # perf trace -vv --no-syscalls --max-stack 4 -e probe_libc:inet_pton/call-graph=dwarf/ ping -6 -c 1 ::1
  callchain: type DWARF
  callchain: stack dump size 8192
  perf_event_attr:
    type                             2
    size                             112
    config                           0x730
    { sample_period, sample_freq }   1
    sample_type                      IP|TID|TIME|ADDR|CALLCHAIN|CPU|PERIOD|RAW|REGS_USER|STACK_USER|DATA_SRC
    exclude_callchain_user           1
    { wakeup_events, wakeup_watermark } 1
    sample_regs_user                 0xff0fff
    sample_stack_user                8192
    sample_max_stack                 50656
  sys_perf_event_open failed, error -75
  Value too large for defined data type
  # perf trace -vv --no-syscalls --max-stack 4 -e probe_libc:inet_pton/call-graph=dwarf/ ping -6 -c 1 ::1
  callchain: type DWARF
  callchain: stack dump size 8192
  perf_event_attr:
    type                             2
    size                             112
    config                           0x730
    sample_type                      IP|TID|TIME|ADDR|CALLCHAIN|CPU|PERIOD|RAW|REGS_USER|STACK_USER|DATA_SRC
    exclude_callchain_user           1
    sample_regs_user                 0xff0fff
    sample_stack_user                8192
    sample_max_stack                 30448
  sys_perf_event_open failed, error -75
  Value too large for defined data type
  #

Now the attr.sample_max_stack is set to zero and the above works as
expected:

  # perf trace --no-syscalls --max-stack 4 -e probe_libc:inet_pton/call-graph=dwarf/ ping -6 -c 1 ::1
  PING ::1(::1) 56 data bytes
  64 bytes from ::1: icmp_seq=1 ttl=64 time=0.072 ms

  --- ::1 ping statistics ---
  1 packets transmitted, 1 received, 0% packet loss, time 0ms
  rtt min/avg/max/mdev = 0.072/0.072/0.072/0.000 ms
       0.000 probe_libc:inet_pton:(7feb7a998350))
                                         __inet_pton (inlined)
                                         gaih_inet.constprop.7 (/usr/lib64/libc-2.26.so)
                                         __GI_getaddrinfo (inlined)
                                         [0xffffaa39b6108f3f] (/usr/bin/ping)
  #

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Hendrick Brueckner <brueckner@linux.vnet.ibm.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Thomas Richter <tmricht@linux.vnet.ibm.com>
Cc: Wang Nan <wangnan0@huawei.com>
Link: https://lkml.kernel.org/n/tip-is9tramondqa9jlxxsgcm9iz@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>