BUG/MEDIUM: config: properly adjust maxconn with nbproc when memmax is forced

BUG/MEDIUM: config: properly adjust maxconn with nbproc when memmax is forced

When memmax is forced using "-m", the per-process memory limit is enforced
using setrlimit(), but this value is not used to compute the automatic
maxconn limit. In addition, the per-process memory limit didn't consider
the fact that the shared SSL cache only needs to be accounted once.

The doc was also fixed to clearly state that "-m" is global and not per
process. It makes sense because people who use -m want to protect the
system's resources regardless of whatever appears in the configuration.