Fix a few typo/compilation problems.
net/: Remove all CONFIG_NET_xxx_TCP_RECVWNDO configuration variables. They were used only to initialize the d_recwndo of the network device structure which no longer exists.
net/: Remove the device TCP receive window field (d_recvwndo) from the device structure. That value is no longer retained, but is calculated dynamically.
Remove some dangling references to CONFIG_NET_TCP_RWND_CONTROL.
net/tcp: Take read-ahead throttling into account when calculating the TCP receive window size.
net/tcp: tcp_get_recvwindow() now returns the receive window size directly (vs. indirectly via the device structure).
net/tcp: Remove CONFIG_NET_TCP_RWND_CONTROL. TCP window algorithm is now trigged only by CONFIG_NET_TCP_READAHEAD.