ringaccount: make value Id distribution non-static

This minor cleanup and performance/memory optimization
replaces the static ID distribution by a type shortcut.
Integer distributions are typically stateless and
are fully optimized-out by the compiler, which was
prevented by the static variable.

Change-Id: I9f75acf57662c7f30404586feea3049d96ce1ca9
Reviewed-by: Guillaume Roguez <guillaume.roguez@savoirfairelinux.com>