package/openldap: needs MMU

openldap uses fork(), so needs an MMU.

Fixes:
    http://autobuild.buildroot.org/results/8a7/8a72aef6525da27b92235b918b6d41ad1c7fac09/
    http://autobuild.buildroot.org/results/1ce/1ce0ac525217fc5308ea510c997c7ac59e69bc4c/
    http://autobuild.buildroot.org/results/0eb/0eb180f77d5b70886e062ada1be133916ac97c31/



Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>