[ACKVEC]: Reduce length of identifiers

This is reduces the length of the struct ackvec/ackvec_record fields. It is
a purely text-based replacement:

	s#dccpavr_#avr_#g;
	s#dccpav_#av_#g;

and increases readability somewhat.

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>