To maintain compatibility with userspace tools, the field length must not
be included in the template digest calculation for the 'ima' template.

Fixes commit: a71dc65d ima: switch to new template management mechanism
Signed-off-by: NRoberto Sassu <roberto.sassu@polito.it>
Signed-off-by: NMimi Zohar <zohar@linux.vnet.ibm.com>