Add frameworks/opt/net/wifi to root.bp

This commit add frameworks/opt/net/wifi to root.bp so that
libwifi-system.so can become vendor_available.

Test: mmm frameworks/opt/net/wifi
Bug: 37429084
Change-Id: I98c695ec6b6c3e6788681b5dc243adab4d29d094
diff --git a/root.bp b/root.bp
index 4f9775b..4c29f4d 100644
--- a/root.bp
+++ b/root.bp
@@ -20,6 +20,7 @@
     "frameworks/*",
     "frameworks/compile/*",
     "frameworks/hardware/interfaces",
+    "frameworks/opt/net/wifi",
     "hardware/*",
     "libcore",
     "libnativehelper",