SSH2: Update timeout functionality

Make it so Net_SSH2 doesn't close channel upon timeout. only if reset() is closed will channel be closed.
Also add isTimeout() function
Merge pull request #117 from bantu/elliptic-curve-preparation

Preparation for ECDH in SSH
[feature/elliptic-curve] Rudimentary ECDH implementation for SSH.
[feature/elliptic-curve] Some very basic test on the P192 and P224 NIST curves.