Move netd.c to Tethering module

This is a clean move. The content of netd.c is not changed. The object
name is still netd.o. But the module name is renamed to netd.o_mainline
to avoid name collision in sc-mainline-prod branch.

Modified Android.bp according to the file location. The sub_dir is
newly specified. The object file will be compiled to:
- apex/com.android.tethering/etc/bpf/net_shared/netd.o

The extracted programs and maps will be in:
- sys/fs/bpf/net_shared/

The netd.o will not be loaded in pre-T because the bpfloader before T
does not load objects from paths other than:
- apex/com.android.tethering/etc/bpf/
- /system/etc/bpf/

Bug: 202086915
Test: cd system/netd; atest
Test: atest TrafficStatsTest NetworkUsageStatsTest
Change-Id: I5281c851341f9258a37d8aad6da4196c06342940
diff --git a/bpf_progs/Android.bp b/bpf_progs/Android.bp
index d015ef6..4fa288b 100644
--- a/bpf_progs/Android.bp
+++ b/bpf_progs/Android.bp
@@ -71,3 +71,16 @@
         "-Werror",
     ],
 }
+
+bpf {
+    name: "netd.o_mainline",
+    srcs: ["netd.c"],
+    cflags: [
+        "-Wall",
+        "-Werror",
+    ],
+    include_dirs: [
+        "frameworks/libs/net/common/netd/libnetdutils/include",
+    ],
+    sub_dir: "net_shared",
+}