Write Data Saver setting to BPF map

The information is needed by modules who want to know whether a
specific UID is blocked by Data Saver feature.

1. Add a one-element map data_saver_enabled_map.
2. Update current data saver setting to the map.

Bug: 288340533
Test: atest FrameworksNetTests:android.net.connectivity.com.android.serv
er.BpfNetMapsTest
Test: atest bpf_existence_test

Change-Id: I981da4b569247c33cba2d365cb6f2691f673474e
diff --git a/bpf_progs/netd.c b/bpf_progs/netd.c
index b77a8d1..5759df7 100644
--- a/bpf_progs/netd.c
+++ b/bpf_progs/netd.c
@@ -112,6 +112,9 @@
                        BPFLOADER_IGNORED_ON_VERSION, BPFLOADER_MAX_VER, LOAD_ON_ENG,
                        LOAD_ON_USER, LOAD_ON_USERDEBUG);
 
+DEFINE_BPF_MAP_RO_NETD(data_saver_enabled_map, ARRAY, uint32_t, bool,
+                       DATA_SAVER_ENABLED_MAP_SIZE)
+
 // iptables xt_bpf programs need to be usable by both netd and netutils_wrappers
 // selinux contexts, because even non-xt_bpf iptables mutations are implemented as
 // a full table dump, followed by an update in userspace, and then a reload into the kernel,