As a general rule, we're trying to migrate checking for specific library features out of Autoconf and into gnulib or whereever. This is true for POSIX interfaces as well as for non-POSIX; for example, it's why AC_FUNC_FNMATCH is marked as an obsolescent macro in Autoconf. (I'd like to remove more of these macros from Autoconf as well, at some point.) Any improvements for network-related library functions are probably better suited for the package that needs them, or for gnulib.
Perhaps Autoconf needs to support a general feature for checking library features, which could be used by gnulib or whatever to check for specific features, but we'd need some implementation experience to know what that feature would be.
