hooks.c: also add a matching sysconf for _SC_NPROCESSORS_ONLN

Used by libstagefright.

Signed-off-by: Ricardo Salveti de Araujo <ricardo.salveti@canonical.com>
Merge pull request #123 from rsalveti/sysconf_nprocessors_onln

hooks.c: also add a matching sysconf for _SC_NPROCESSORS_ONLN