r3278: - rewrote the client side rpc connection code to use lib/socket/

r3278: - rewrote the client side rpc connection code to use lib/socket/
  rather than doing everything itself. This greatly simplifies the
  code, although I really don't like the socket_recv() interface (it
  always allocates memory for you, which means an extra memcpy in this
  code)

- fixed several bugs in the socket_ipv4.c code, in particular client
  side code used a non-blocking connect but didn't handle EINPROGRESS,
  so it had no chance of working. Also fixed the error codes, using
  map_nt_error_from_unix()

- cleaned up and expanded map_nt_error_from_unix()

- changed interpret_addr2() to not take a mem_ctx. It makes absolutely
  no sense to allocate a fixed size 4 byte structure like this. Dozens
  of places in the code were also using interpret_addr2() incorrectly
  (precisely because the allocation made no sense)
(This used to be commit 7f2c771b0e0e98c5c9e5cf662592d64d34ff1205)