asterisk.c: Fix sending incorrect messages to systemd notify

Send "RELOADING=1" instead of "RELOAD=1" to follow the format
expected by systemd (see sd_notify(3) man page).

Do not send STOPPING=1 in remote console mode:
attempting to execute "asterisk -rx" by the main process leads to
a warning if NotifyAccess=main (the default) or to a forced termination
if NotifyAccess=all.

(cherry picked from commit d3ff7c3eee6f1130b20e640f5fb60da7c797ebe1)