refactor: simplify push{string,number}field and clients.

* ext/include/_helpers.c (pushnumberfield, pushstringfield):
Reimplement as macros, with fewer arguments required.  Adjust all
callers.
* ext/posix/sys/socket.c (sockaddr_to_lua): Renamed from this...
(pushsockaddrinfo): ...to this, and simplify considerably.  Adjust
all callers.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>