internal/netlink: isolate receive method

This enables use with epoll for receiving events only.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/netlink/netlink.go

@@ -156,9 +156,18 @@ func (c *conn) Roundtrip(f func(msg *syscall.NetlinkMessage) error) error {
 		return os.NewSyscallError("sendto", err)
 	}
 
+	return c.receive(f, 0)
+}
+
+// receive receives from a socket with specified flags until a non-nil error is
+// returned by f. An error of type [Complete] is returned as nil.
+func (c *conn) receive(
+	f func(msg *syscall.NetlinkMessage) error,
+	flags int,
+) error {
 	for {
 		buf := c.buf
-		if n, _, err := syscall.Recvfrom(c.fd, buf, 0); err != nil {
+		if n, _, err := syscall.Recvfrom(c.fd, buf, flags); err != nil {
 			return os.NewSyscallError("recvfrom", err)
 		} else if n < syscall.NLMSG_HDRLEN {
 			return syscall.EBADE