MEDIUM: initcall: move STG_REGISTER earlier

MEDIUM: initcall: move STG_REGISTER earlier

The STG_REGISTER init level is used to register known keywords and
protocol stacks. It must be called earlier because some of the init
code already relies on it to be known. For example, "haproxy -vv"
for now is constrained to start very late only because of this.

This patch moves it between STG_LOCK and STG_ALLOC, which is fine as
it's used for static registration.