net: dccp: Fix ccid2_rtt_estimator() kernel-doc

make C=1 reports:

warning: Function parameter or struct member 'mrtt' not described in 'ccid2_rtt_estimator'

So document the 'mrtt' parameter.
Signed-off-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://lore.kernel.org/r/20240505-ccid2_rtt_estimator-kdoc-v1-1-09231fcb9145@quicinc.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/dccp/ccids/ccid2.c

@@ -353,6 +353,7 @@ static void ccid2_hc_tx_packet_sent(struct sock *sk, unsigned int len)
 /**
  * ccid2_rtt_estimator - Sample RTT and compute RTO using RFC2988 algorithm
  * @sk: socket to perform estimator on
+ * @mrtt: measured RTT
  *
  * This code is almost identical with TCP's tcp_rtt_estimator(), since
  * - it has a higher sampling frequency (recommended by RFC 1323),