Fix for only SSH or TLS enabled
Fix for only SSH or TLS enabled

When only NC_ENABLED_SSH defined, NC_TI_OPENSSL does not exist in
enumeration type NC_TRANSPORT_IMPL. Similarly, when only NC_ENABLED_TLS
defined, NC_TI_LIBSSH does not exist in NC_TRANSPORT_IMPL.

So we have to re-factor this code excerpt for compilation.

CESNET/Netopeer2,CESNET/Netopeer2