In both the sender and the receiver it is possible that the stored
RTT value is accessed before an actual RTT estimate has been computed.

This patch
 * initialises the sender RTT to 0
     - the sender always accesses the RTT in ccid3_hc_tx_packet_sent
     - the RTT is further needed for the window counter algorithm

 * replaces the receiver initialisation of 5msec with 0
     - which has the same effect and removes an `XXX'
     - the RTT value is needed in ccid3_hc_rx_packet_recv as rtt_prev
Signed-off-by: NGerrit Renker <gerrit@erg.abdn.ac.uk>
Acked-by: NIan McDonald <ian.mcdonald@jandi.co.nz>
Signed-off-by: NArnaldo Carvalho de Melo <acme@mandriva.com>