Defines the default receive window size in bytes. Refer to Per-Route Metrics for a discussion of setting
a different value on a per-route basis. See also tcp_max_buf and tcp_recv_hiwat_minmss.
2048 to 1,073,741,824
An application can use setsockopt(3XNET) SO_RCVBUF to
change the individual connection's receive buffer.