fix data race when getting capabilities from neighbor config

Func capabilitiesFromConfig was always taken under the read lock.
However, when graceful restart is enabled for some families, this
function writes to the neighbor config which creates a data race.

pkg/server/fsm.go

@@ -1254,9 +1254,9 @@ func open2Cap(open *bgp.BGPOpen, n *oc.Neighbor) (map[bgp.BGPCapabilityCode][]bg
 func (h *fsmHandler) opensent(ctx context.Context) (bgp.FSMState, *fsmStateReason) {
 	fsm := h.fsm
 
-	fsm.lock.RLock()
+	fsm.lock.Lock()
 	m := buildopen(fsm.gConf, fsm.pConf)
-	fsm.lock.RUnlock()
+	fsm.lock.Unlock()
 
 	b, _ := m.Serialize()
 	fsm.conn.Write(b)

pkg/server/server.go

@@ -864,8 +864,11 @@ func (s *BgpServer) toConfig(peer *peer, getAdvertised bool) *oc.Neighbor {
 
 	conf.State.RemoteCapabilityList = remoteCap
 
-	peer.fsm.lock.RLock()
+	peer.fsm.lock.Lock()
 	conf.State.LocalCapabilityList = capabilitiesFromConfig(peer.fsm.pConf)
+	peer.fsm.lock.Unlock()
+
+	peer.fsm.lock.RLock()
 	conf.State.SessionState = oc.IntToSessionStateMap[int(peer.fsm.state)]
 	conf.State.AdminState = oc.IntToAdminStateMap[int(peer.fsm.adminState)]
 	state := peer.fsm.state
@@ -948,12 +951,15 @@ func newWatchEventPeer(peer *peer, m *fsmMsg, oldState bgp.FSMState, t PeerEvent
 	var laddr string
 	var rport, lport uint16
 
+	peer.fsm.lock.Lock()
+	sentOpen := buildopen(peer.fsm.gConf, peer.fsm.pConf)
+	peer.fsm.lock.Unlock()
+
 	peer.fsm.lock.RLock()
 	if peer.fsm.conn != nil {
 		_, rport = peer.fsm.RemoteHostPort()
 		laddr, lport = peer.fsm.LocalHostPort()
 	}
-	sentOpen := buildopen(peer.fsm.gConf, peer.fsm.pConf)
 	recvOpen := peer.fsm.recvOpen
 	e := &watchEventPeer{
 		Type:          t,