OffloadUtils - implement getTetherIngressProgFd()

Test: build, atest
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: Ibbc655a483507624c2b340bdb7f3f0b311a90722
diff --git a/server/OffloadUtils.h b/server/OffloadUtils.h
index 3c578d0..f2a4dc2 100644
--- a/server/OffloadUtils.h
+++ b/server/OffloadUtils.h
@@ -57,6 +57,13 @@
     return (fd == -1) ? -errno : fd;
 }
 
+inline int getTetherIngressProgFd(bool with_ethernet_header) {
+    const int fd = bpf::bpfFdGet(
+            with_ethernet_header ? TETHER_INGRESS_PROG_ETHER_PATH : TETHER_INGRESS_PROG_RAWIP_PATH,
+            0);
+    return (fd == -1) ? -errno : fd;
+}
+
 int openNetlinkSocket(void);
 
 int doTcQdiscClsact(int fd, int ifIndex, uint16_t nlMsgType, uint16_t nlMsgFlags);