Add missing libc++ includes

Bug: 175635923
Test: m MODULES-IN-packages-modules-Connectivity
Change-Id: I94dafe991ccd73450671ea68eaf65b787dc1d0fa
diff --git a/staticlibs/netd/libnetdutils/include/netdutils/Log.h b/staticlibs/netd/libnetdutils/include/netdutils/Log.h
index 77ae649..d266cbc 100644
--- a/staticlibs/netd/libnetdutils/include/netdutils/Log.h
+++ b/staticlibs/netd/libnetdutils/include/netdutils/Log.h
@@ -19,6 +19,7 @@
 
 #include <chrono>
 #include <deque>
+#include <functional>
 #include <shared_mutex>
 #include <string>
 #include <type_traits>