Re-enable the OSI memory allocation tracker.

Previously, the OSI memory allocation tracker was disabled as
a temporary workaround for Bug 21561735.
The root cause for the original issue is now addressed by using the
appropriate linker flags when generating the bluetooth.default.so
shared library:

  LOCAL_LDLIBS := -Wl,-Bsymbolic,-Bsymbolic-functions

Also, added missing #include in file "btif/src/btif_sock_sco.c"

Bug: 21561735
Change-Id: I384a6f3d1d03c74f8d1e3c96bf7e0b5961206feb
diff --git a/main/Android.mk b/main/Android.mk
index 04d4332..ff7b4a5 100644
--- a/main/Android.mk
+++ b/main/Android.mk
@@ -151,6 +151,16 @@
 LOCAL_MODULE_RELATIVE_PATH := hw
 LOCAL_MODULE_TAGS := optional
 LOCAL_MODULE_CLASS := SHARED_LIBRARIES
+
+#
+# Shared library link options.
+# References to global symbols and functions should bind to the library
+# itself. This is to avoid issues with some of the unit/system tests
+# that might link statically with some of the code in the library, and
+# also dlopen(3) the shared library.
+#
+LOCAL_LDLIBS := -Wl,-Bsymbolic,-Bsymbolic-functions
+
 LOCAL_REQUIRED_MODULES := \
     auto_pair_devlist.conf \
     bt_did.conf \