Fix GH-8674: sockets extension won't build for older Linux kernels

In abscence of the needed header, disable the feature altogether.

Closes GH-8677.

Author: devnexen

configure.ac

@@ -395,6 +395,7 @@ fcntl.h \
 grp.h \
 ieeefp.h \
 langinfo.h \
+linux/sock_diag.h \
 malloc.h \
 poll.h \
 pty.h \

ext/sockets/sockets.c

@@ -55,8 +55,10 @@
 # if HAVE_IF_NAMETOINDEX
 #  include <net/if.h>
 # endif
-# ifdef SO_MEMINFO
+# if defined(HAVE_LINUX_SOCK_DIAG_H)
 #  include <linux/sock_diag.h>
+# else
+#  undef SO_MEMINFO
 # endif
 #endif