eal: remove experimental flag of hotplug functions

eal: remove experimental flag of hotplug functions

These functions are quite old and are the only available replacement
for the deprecated attach/detach functions.

Note: some new functions may (again) replace these hotplug functions,
in future, with better parameters.

Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
Reviewed-by: Andrew Rybchenko <arybchenko@solarflare.com>
Acked-by: Gaetan Rivet <gaetan.rivet@6wind.com>
Reviewed-by: Stephen Hemminger <stephen@networkplumber.org>