Avoid overwriting blocking reason
Avoid overwriting blocking reason

When a path is blocked for 'NO_FEASIBLE_MODE' reason, and bidir is true,
the request attributes are filled with the last explored mode values
(baudrate notably), and the reversed path is propagated with this last
explored mode specs. if this reversed path is also not feasible the blocking
reason was overwritten with a 'MODE_NOT_FESIBLE' reasonn, because
baudrate is filled in the request attribute.

This change ensure that the blocking reason (if it exists) is not overwritten.

Signed-off-by: EstherLerouzic <9136e9bbec0a09a1685b8ebbe677b6c9b26e8f18@orange.com>
Change-Id: If80a37d77e2b967a327562c733a44e7f78f1c544

Telecominfraproject/gnpy