ip_vs.h: fix implicit use of module_get/module_put from module.h

ip_vs.h: fix implicit use of module_get/module_put from module.h

This file was using the module get/put functions in two simple inline
functions.  But module_get/put were only within scope because of
the implicit presence of module.h being everywhere.

Rather than add module.h to another file in include/  -- which is
exactly the thing we are trying to avoid, simply convert these
one-line functions into a define, as per what was done for the
device_schedule_callback() in commit 523ded71de0c5e669733.

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>