MODRESTART: Defer restart to the event loop

MODRESTART: Defer restart to the event loop

When a remote MODRESTART command is received, it will pass through the
ENCAP module. The ms_encap function is responsible for dispatching the
command handler and then the modules will eventually be reloaded.

However, if the ENCAP module is reloaded to a different address, the
stack now contains the address of a function that no longer exists.

Return immediately from the command handler and have the event loop
call the function responsible for reloading the modules instead.

Reported-by: mniip (Freenode)