The BEGIN_SELECT_LOOP and END_SELECT_LOOP macros of socketmodule.c don't handle
EINTR. Functions using these macros use an inner loop to handle EINTR, but they
don't recompute the timeout.

This changes replaces the two macros with a new sock_call() function which
takes a function as a parameter. sock_call() recomputes the timeout, handle
false positive and handle EINTR.