As described in issue #1695, on 4.17 for syscalls on x86,
both sys_<fnname> and SyS_<fnname> are gone, the replacements
are __ia32_sys_sync and __x64_sys_sync.
The commit in Linus tree:
https://github.com/torvalds/linux/commit/d5a00528b58cdb2c71206e18bd021e34c4eab878

This patch introduced two APIs for python BPF object.
The API get_syscall_prefix() returns the prefix "sys_"/"__x64_sys_".
The API get_syscall_fnname(name) returns kernel function name for the syscall,
e.g., on x64, get_syscall_fnname("clone") will return "sys_clone" if kernel
has it, otherwise, "__x64_sys_clone".
get_syscall_prefix() is mostly useful for the regex func specifier of
attach_kprobe().

This patch only fixed the code using python API on examples and tests directory.

TOTO: python on tools directory, C++ and lua
Signed-off-by: Yonghong Song <yhs@fb.com>