test_bpf: Fix a new clang warning about xor-ing two numbers

r369217 in clang added a new warning about potential misuse of the xor
operator as an exponentiation operator:

../lib/test_bpf.c:870:13: warning: result of '10 ^ 300' is 294; did you
mean '1e300'? [-Wxor-used-as-pow]
                { { 4, 10 ^ 300 }, { 20, 10 ^ 300 } },
                       ~~~^~~~~
                       1e300
../lib/test_bpf.c:870:13: note: replace expression with '0xA ^ 300' to
silence this warning
../lib/test_bpf.c:870:31: warning: result of '10 ^ 300' is 294; did you
mean '1e300'? [-Wxor-used-as-pow]
                { { 4, 10 ^ 300 }, { 20, 10 ^ 300 } },
                                         ~~~^~~~~
                                         1e300
../lib/test_bpf.c:870:31: note: replace expression with '0xA ^ 300' to
silence this warning

The commit link for this new warning has some good logic behind wanting
to add it but this instance appears to be a false positive. Adopt its
suggestion to silence the warning but not change the code. According to
the differential review link in the clang commit, GCC may eventually
adopt this warning as well.

Link: https://github.com/ClangBuiltLinux/linux/issues/643
Link: https://github.com/llvm/llvm-project/commit/920890e26812f808a74c60ebc14cc636dac661c1
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Acked-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>