This time, socket's buffer lock requires solock() to be held. As a part of

This time, socket's buffer lock requires solock() to be held. As a part of
socket buffers standalone locking work, move socket state bits which
represent its buffers state to per buffer state. Introduce `sb_state' and
turn SS_CANTSENDMORE to SBS_CANTSENDMORE. This bit will be processed on
`so_snd' buffer only.

Move SS_CANTRCVMORE and SS_RCVATMARK bits with separate diff to make
review easier and exclude possible so_rcv/so_snd mistypes.

Also, don't adjust the remaining SS_* bits right now.

ok millert@