dcap: drop READV io log level from info to debug

Ticket: #7980
Acked-by: Paul Millar
Target: master, 2.6
Require-book: no
Require-notes: yes
Signed-off-by: Tigran Mkrtchyan <tigran.mkrtchyan@desy.de>
Merge pull request #156 from kofemann/dcap-fix-2.6

drop log level for READV