Se corrige el envío de 491 en la recepción de invites.
Se crea la variable glareinvite.
int glareinvite; /*!< A invite received while a pending invite is already present is stored here. Its seqno is the
value. Since this glare invite's seqno is not the same as the pending invite's, it must be
held in order to properly process acknowledgements for our 491 response. */
channels/chan_sip.c