BUG-632: add TCP-MD5 configuration fragments

This patch adds the prerequisite TCP-MD5 configuration fragments, which
are optionally referred to by both BGP and PCEP configuration.

Change-Id: Ie3c93ba5840a198f5a814e92c514748acd2f4cda
Signed-off-by: Robert Varga <rovarga@cisco.com>
Merge "BUG-632: add TCP-MD5 configuration fragments"