perf trace beauty: Allow syscalls to mask an argument before considering it

Take mount's 'flags' arg, to cope with this semantic, as defined in do_mount in fs/namespace.c:

  /*
   * Pre-0.97 versions of mount() didn't have a flags word.  When the
   * flags word was introduced its top half was required to have the
   * magic value 0xC0ED, and this remained so until 2.4.0-test9.
   * Therefore, if this magic number is present, it carries no
   * information and must be discarded.
   */

We need to mask this arg, and then see if it is zero, when we simply
don't print the arg name and value.

The next patch will use this for mount's 'flag' arg.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Benjamin Peterson <benjamin@python.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: https://lkml.kernel.org/n/tip-btue14k5jemayuykfrwsnh85@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>