BUG/MAJOR: init: properly compute the default global.maxpipes value

BUG/MAJOR: init: properly compute the default global.maxpipes value

Initial default settings for maxconn/maxsock/maxpipes were rearranged
in commit a409f30d0 ("MINOR: init: move the maxsock calculation code
to compute_ideal_maxsock()") but as a side effect, the calculated
maxpipes value was not stored anymore into global.maxpipes. This
resulted in splicing being disabled unless there is an explicit
maxpipes setting in the global section.

This patch just stores the calculated ideal value as planned in the
computation and as was done before the patch above.

This is strictly 2.2, no backport is needed.