When correcting conversion issues in RouteBase a to_string bug was
introduced which caused some characters to be escaped when inserted
to the string, for example a prefix_len of 0 would render as "\0"
rather than inserting '0'. The std::ios::binary flag does not seem
to prevent this for std::ostringstream so I have cast the data member
up to uint16_t which should be safe, and solves the issue.
Added a unit test to demonstrate the issue. Old code output was
"0.0.0.0/\0", now outputs "0.0.0.0/0" as expected.
Signed-off-by: Charlie Vigue <charlie.vigue@openvpn.com>