service: fix return values of functions to 0 or 1

Previously to this commit, the return value of the following
functions was the mask value, instead of a neat 0 or 1.

This commit fixes this using the "!!" trick, to force the
number to 1 instead of the bitmask value itself, bringing
the return value in line with the function documentation.

Fixes: 21698354c832 ("service: introduce service cores concept")

Signed-off-by: Harry van Haaren <harry.van.haaren@intel.com>
Acked-by: Pavan Nikhilesh <pbhagavatula@caviumnetworks.com>