tools/bpftool: ignore build products

For untracked things of tools/bpf, add this.

Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Taeung Song <treeze.taeung@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
diff --git a/tools/bpf/.gitignore b/tools/bpf/.gitignore
new file mode 100644
index 0000000..dfe2bd5a
--- /dev/null
+++ b/tools/bpf/.gitignore
@@ -0,0 +1,5 @@
+FEATURE-DUMP.bpf
+bpf_asm
+bpf_dbg
+bpf_exp.yacc.*
+bpf_jit_disasm