configure: fix AC_CHECK_FUNCS should use literals

configure: fix AC_CHECK_FUNCS should use literals

Error

    configure.ac:291: warning: AC_CHECK_FUNCS(getnameinfo
    ): you should use literals
    ../autoconf-2.71/lib/autoconf/functions.m4:117: AC_CHECK_FUNCS is expanded from...
    ../autoconf-2.71/lib/m4sugar/m4sh.m4:692: _AS_IF_ELSE is expanded from...
    ../autoconf-2.71/lib/m4sugar/m4sh.m4:699: AS_IF is expanded from...
    configure.ac:291: the top level
    configure.ac:291: warning: AC_CHECK_FUNCS(getprotobynumber
    ): you should use literals
    ../autoconf-2.71/lib/autoconf/functions.m4:117: AC_CHECK_FUNCS is expanded from...
    ../autoconf-2.71/lib/m4sugar/m4sh.m4:692: _AS_IF_ELSE is expanded from...
    ../autoconf-2.71/lib/m4sugar/m4sh.m4:699: AS_IF is expanded from...
    configure.ac:291: the top level
    configure.ac:291: warning: AC_CHECK_FUNCS(getservbyname
    ): you should use literals
    ../autoconf-2.71/lib/autoconf/functions.m4:117: AC_CHECK_FUNCS is expanded from...
    ../autoconf-2.71/lib/m4sugar/m4sh.m4:692: _AS_IF_ELSE is expanded from...
    ../autoconf-2.71/lib/m4sugar/m4sh.m4:699: AS_IF is expanded from...
    configure.ac:291: the top level
    configure.ac:291: warning: AC_CHECK_FUNCS(inet_ntop
    ): you should use literals
    ../autoconf-2.71/lib/autoconf/functions.m4:117: AC_CHECK_FUNCS is expanded from...
    ../autoconf-2.71/lib/m4sugar/m4sh.m4:692: _AS_IF_ELSE is expanded from...
    ../autoconf-2.71/lib/m4sugar/m4sh.m4:699: AS_IF is expanded from...
    configure.ac:291: the top level
    configure.ac:291: warning: AC_CHECK_FUNCS(inet_pton
    ): you should use literals
    ../autoconf-2.71/lib/autoconf/functions.m4:117: AC_CHECK_FUNCS is expanded from...
    ../autoconf-2.71/lib/m4sugar/m4sh.m4:692: _AS_IF_ELSE is expanded from...
    ../autoconf-2.71/lib/m4sugar/m4sh.m4:699: AS_IF is expanded from...
    configure.ac:291: the top level