In case of an error this will have the position in the string the error occured
Sets the priorities to use on the ciphers, key exchange methods,
macs and compression methods. This function avoids keeping a
priority cache and is used to directly set string priorities to a
TLS session. For documentation check the gnutls_priority_init().
On syntax error GNUTLS_E_INVALID_REQUEST is returned,
GNUTLS_E_SUCCESS on success, or an error code.