OML: Fix encoded length value of OML GET ATTRIBUTES

Before this patch, all OML GET ATTRIBUTES messages were encoded with
an erroneous OML header length value.  The length value was always three
bytes less than the actual message length.  This patch fixes the
problem.

Change-Id: I56068de0bb14a99ec39be587e542e27cddb7d1df
Closes: OS#3799
1 file changed