MINOR: peers: Use a static variable to wait a resync on reload

MINOR: peers: Use a static variable to wait a resync on reload

When a process is reloaded, the old process must performed a synchronisation
with the new process. To do so, the sync task notify the local peer to
proceed and waits. Internally, the sync task used PEERS_F_DONOTSTOP flag to
know it should wait. However, this flag was only set/unset in a single
function. There is no real reason to set a flag to do so. A static variable
set to 1 when the resync starts and to 0 when it is finished is enough.