ssh2: fix int overflow with timeout

As mina sshd used int as timeout value, max long
converted into negative number and ignored.

Acked-by: Paul Millar
Target: master
Require-book: no
Require-notes: no
(cherry picked from commit 8608b98be3206351acda3a8e4389b072f2df089e)
Signed-off-by: Tigran Mkrtchyan <tigran.mkrtchyan@desy.de>
Merge pull request #297 from kofemann/ssh-overflow

ssh2: fix int overflow with timeout