[client] Use unique sequence numbers for bsd routes (#4081)

updates the route manager on Unix to use a unique, incrementing sequence number for each route message instead of a fixed value.

Replace the static Seq: 1 with a call to r.getSeq()
Add an atomic seq field and the getSeq method in SysOps

client/internal/routemanager/systemops/systemops.go

@@ -5,6 +5,7 @@ import (
 	"net"
 	"net/netip"
 	"sync"
+	"sync/atomic"
 
 	"github.com/netbirdio/netbird/client/iface/wgaddr"
 	"github.com/netbirdio/netbird/client/internal/routemanager/notifier"
@@ -52,6 +53,9 @@ type SysOps struct {
 	mu sync.Mutex
 	// notifier is used to notify the system of route changes (also used on mobile)
 	notifier *notifier.Notifier
+	// seq is an atomic counter for generating unique sequence numbers for route messages
+	//nolint:unused // only used on BSD systems
+	seq atomic.Uint32
 }
 
 func NewSysOps(wgInterface wgIface, notifier *notifier.Notifier) *SysOps {
@@ -61,6 +65,11 @@ func NewSysOps(wgInterface wgIface, notifier *notifier.Notifier) *SysOps {
 	}
 }
 
+//nolint:unused // only used on BSD systems
+func (r *SysOps) getSeq() int {
+	return int(r.seq.Add(1))
+}
+
 func (r *SysOps) validateRoute(prefix netip.Prefix) error {
 	addr := prefix.Addr()
 

client/internal/routemanager/systemops/systemops_unix.go

@@ -108,7 +108,7 @@ func (r *SysOps) buildRouteMessage(action int, prefix netip.Prefix, nexthop Next
 		Type:    action,
 		Flags:   unix.RTF_UP,
 		Version: unix.RTM_VERSION,
-		Seq:     1,
+		Seq:     r.getSeq(),
 	}
 
 	const numAddrs = unix.RTAX_NETMASK + 1