Compile native network functionis into libandroid_net.

libandroid includes some local implementations, but depends on many
other libraries to provide those (counting transitive dependencies, a
total of 65). This patch copies the native network functions provided
by android/multinetwork.h header to its own new libandroid_net shared
library. This new library has only one other shared library dependency.

Bug: 32842753
Test: `make` on aosp_arm-eng
Change-Id: Ifbd529d9bf74a8d4f754733cff345729de6b1521

native/android/Android.mk

@@ -1,6 +1,8 @@
 BASE_PATH := $(call my-dir)
 LOCAL_PATH:= $(call my-dir)
 
+common_cflags := -Wall -Werror -Wunused -Wunreachable-code
+
 include $(CLEAR_VARS)
 
 # our source files
@@ -42,6 +44,23 @@ LOCAL_C_INCLUDES += \
 
 LOCAL_MODULE := libandroid
 
-LOCAL_CFLAGS += -Wall -Werror -Wunused -Wunreachable-code
+LOCAL_CFLAGS += $(common_cflags)
+
+include $(BUILD_SHARED_LIBRARY)
+
+# Network library.
+include $(CLEAR_VARS)
+LOCAL_MODULE := libandroid_net
+LOCAL_CFLAGS := $(common_cflags)
+LOCAL_SRC_FILES:= \
+    net.c \
+
+LOCAL_SHARED_LIBRARIES := \
+    libnetd_client \
+
+LOCAL_C_INCLUDES += \
+    frameworks/base/native/include \
+    bionic/libc/dns/include \
+    system/netd/include \
 
 include $(BUILD_SHARED_LIBRARY)