only set 'bpf.progs_loaded' property on eBPF capable devices...

... which also means waitForProgsLoaded() has to be a no-op on pre-bpf devices.

This is more consistent: it's weird to have bpf.progs_loaded set on a 4.4 device.

Test: builds, atest
Bug: 150040815
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: Iddabcf56c187ea518dd2e4d8db451b2f6902aa8e
diff --git a/libbpf_android/Loader.cpp b/libbpf_android/Loader.cpp
index f808dc6..4244eb7 100644
--- a/libbpf_android/Loader.cpp
+++ b/libbpf_android/Loader.cpp
@@ -650,6 +650,8 @@
 }
 
 void waitForProgsLoaded() {
+    if (!android::bpf::isBpfSupported()) return;
+
     while (!android::base::WaitForProperty("bpf.progs_loaded", "1", std::chrono::seconds(5))) {
         ALOGW("Waited 5s for bpf.progs_loaded, still waiting...");
     }