cxgbe tom: Call t4_rcvd_locked from do_rx_data to return RX credits

[jhb]

Summary

In particular, the kernel RPC layer used by the NFS client never
invokes pru_rcvd since it always reads data from the socket upcall
via MSG_SOCALLBCK which avoids calling pru_rcvd. As a result, on an
NFS client connection managed by t4_tom, RX credits were never
returned to the TOE connection to open the TCP window resulting in
connection hangs.

To fix, expand the set of conditions in do_rx_data where RX credits
are returned to match those in t4_rcvd_locked by calling the function
directly.