update BSD sockets implementation to use optimized networking buffers

[laperie]

In order to fully benefit from new networking buffers, BSD sockets needs to be re-implemented using the new net_buf

[tautologyclub]

Anyone mind pasting a link to discussion/PR on "new net_buf"?

[laperie]

Anyone mind pasting a link to discussion/PR on "new net_buf"?

You can monitor progress of this work in #7578

[pfalcon]

@tbursztyka: This can be effectively closed now, right? (Thanks btw for taking charge of consistent upgrade of the all parts of the stack to new API.)

[tbursztyka]

already in now sockets pushes the buf/len to net_context. closing