Really expose the new NDK socket tagging functions added in T.

These functions were already exposed as part of libandroid_net,
but that is not really part of the NDK.

Expose them in libandroid as well, so apps can actually use them.
This is consistent with all the other native networking APIs,
which are exposed in both libandroid_net and libandroid.

Test: atest CtsNativeNetPlatformTestCases
Test: strings out/target/product/bramble/system/lib64/libandroid.so | grep android_tag
Change-Id: I2273cdd48b30a88b82eb3af838031d9fe8897442