android-getifaddrs: Addressing critical compiler warning

* warning: initializer element is not computable at load time
android-getifaddrs: Addresing ISO C90 related warnings

* C++ style comments are not allowed in ISO C90
* ISO C90 forbids mixed declarations and code
android-getifaddrs: Removing unused variables
android-getifadds: Bring code comments back in an ISO C90-compliant way
android-getifaddrs: Updating linux-core.c

* Updating the way we check if we are building for Android to include
the appropiate ifaddrs header dynamically.
* Removing old HAVE_IFADDRS_H condition from the code.
android-getifaddrs: Renaming file as android-ifaddrs

* Updatding source code according to the new name
android-getifaddrs: Cleaning up android-ifaddrs.c
android-getifaddrs: Updating LICENSE