[DCCP]: Collapse repeated `len' statements into one

This replaces 4 individual assignments for `len' with a single
one, placed where the control flow of those 4 leads to.

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