kea: fix compilation with libcxx

Boost headers try to include experimental/string_view when std is less
than c++17. This does not work ith libcxx where this header is not
present.

Refreshed patches.

Signed-off-by: Rosen Penev <rosenp@gmail.com>

net/kea/patches/002-fix-host-compile.patch

@@ -1,6 +1,6 @@
 --- a/m4macros/ax_crypto.m4
 +++ b/m4macros/ax_crypto.m4
-@@ -454,7 +454,7 @@ EOF
+@@ -330,7 +330,7 @@ EOF
      dnl Check availability of SHA-2
      AC_MSG_CHECKING([support of SHA-2])
      LIBS_SAVED=${LIBS}