Check for SS_NBIO in so->so_state instead of sb->sb_flags.

[jhb]

Summary

I noticed this while code reading. I think the only case it would affect
is if you called read() on a non-blocking socket where 0 < sb_cc < sb_lowat
(and the buffer size (uio_resid) was > sb_cc). In that case, you would
block in sbwait() instead of returning a short read.

Test Plan

I have not yet written a test case for this. It would perhaps not be hard
to use TCP_NODELAY on the sender to send 1 byte after the receiver has
raised sb_lowat to 2.

[bz]

Seems correct to me. It's only been like that since 2009 ;-(

[gnn]

Nice catch.

[jhb]

Closed by commit rS275808 (authored by @jhb).