direct_tcpip: bring back inclusion of libssh2_config.h
direct_tcpip: bring back inclusion of libssh2_config.h

In order to increase portability of this example, I'm bringing
the inclusion of libssh2_config.h back, and I also added an
require that header for this example to compile.

I also made all code lines fit within 80 columns.

libssh2/libssh2,libssh2/libssh2,libssh2/libssh2,libssh2/libssh2