vcl: unset fifo events only in read/write
vcl: unset fifo events only in read/write

Avoids accumulation of io event messages when the receiver is slow to
read.

Change-Id: I3a713d339a6ac0781c010be1fbad5a7963ab02c6
Signed-off-by: Florin Coras <c9715e5cdf0718c2e9b10678757dfb027875eba2@cisco.com>

vpp-dev/vpp,vpp-dev/vpp,chrisy/vpp,chrisy/vpp,chrisy/vpp,vpp-dev/vpp,vpp-dev/vpp,vpp-dev/vpp,FDio/vpp,FDio/vpp,vpp-dev/vpp,FDio/vpp,chrisy/vpp,chrisy/vpp,vpp-dev/vpp,FDio/vpp,chrisy/vpp,chrisy/vpp,FDio/vpp,FDio/vpp,chrisy/vpp,FDio/vpp,FDio/vpp