selftests/bpf: ignore build products

Update .gitignore files.

Signed-off-by: Sirio Balmelli <sirio@b-ad.ch>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

tools/bpf/bpftool/.gitignore

@@ -0,0 +1,3 @@
+*.d
+bpftool
+FEATURE-DUMP.bpftool

tools/testing/selftests/bpf/.gitignore

@@ -16,3 +16,4 @@ test_sock
 test_sock_addr
 urandom_read
 test_btf
+test_sockmap