Initial support for RFC2385

Initial support for RFC2385

This brings the ability to manipulate TCP MD5 key attached to a channel
if the underlying operating system supports it.

In order to talk to the underlying OS, we rely on Java Native Interface
(JNI), which contains OS-specific system calls. Currently only Linux is
supported.

Since the JRE libraries insulate Java code from the underlying details,
we also need to muck around implementation-private information within
Channel classes. Currently only openjdk and Oracle JRE is supported.

Change-Id: I664106a96da20ff47ecb71d7b541fe6eb0e056b1
Signed-off-by: Robert Varga <robert.varga@pantheon.sk>
Signed-off-by: Miroslav Miklus <mmiklus@cisco.com>