dccp: schedule an Ack when receiving timestamps

This schedules an Ack when receiving a timestamp, exploiting the
existing inet_csk_schedule_ack() function, saving one case in the
`dccp_ack_pending()' function.

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>

diff --cc net/dccp/dccp.h
Simple merge

diff --cc net/dccp/options.c
Simple merge