net: sockets: tls: Prevent infinite block during handshake

In case peer goes down or we disconnect from the network during the
TLS handshake, the TLS socket may block indefinitely during
connect()/accept(), waiting for data from the peer. This should be
avoided, hence use the preconfigured timeout for the TLS handshake,
same as we use for TCP-level handshake.

Signed-off-by: Robert Lubos <robert.lubos@nordicsemi.no>