Java 1.6 compatibility, minor tweak to cansocket.cpp to provide better android build support.

CanSocket.java was edited to remove any java 1.6 incompatibilities. Some of cansocket.cpp needed to be conditionally wrapped in an extern "C" block to get the Android-NDK to build the .so file correctly. Also, a comment has been added to guide anyone else building against the Android-NDK, as it uses an old version of sys/socket.h and needs to be manually remedied to build, at least as of this pull request.