mwl8787: fix rx aggregate hang

I found RX hanging for unclear reasons.. smoking gun was irq
with no UP_LD_HOST_INT_STATUS bit set, and bitmap 0x0020.
Previous bitmap was 0xe0fe, i.e. 10 frames starting at port
13, and 0x0020 is curiously the 8th frame.  Some more looking
at the trace buffer showed that only 7 bits were set in the
port arg to mwifiex_read_data_sync, and the reason is that
8 ports + control port doesn't fit in the 8 bits we have.

Signed-off-by: Bob Copeland <me@bobcopeland.com>
mwl8787: ask the interface if there's room to tx

Saves some dequeue/requeue rigamarole

Signed-off-by: Bob Copeland <me@bobcopeland.com>