GH-107812: extend socket's netlink support to FreeBSD

on FreeBSD, netlink.h lives under netlink.
Extend the AC_HEADER_CHECK to look there as well.

Author: igalic

Modules/socketmodule.h

@@ -100,6 +100,8 @@ typedef int socklen_t;
 #  include <asm/types.h>
 # endif
 # include <linux/netlink.h>
+#elif defined(HAVE_NETLINK_NETLINK_H)
+# include <netlink/netlink.h>
 #else
 #  undef AF_NETLINK
 #endif

configure

@@ -2880,7 +2880,8 @@ AC_CHECK_HEADERS([net/if.h], [], [],
 ])
 
 # On Linux, netlink.h requires asm/types.h
-AC_CHECK_HEADERS([linux/netlink.h], [], [], [
+# On FreeBSD, netlink.h is located in netlink/netlink.h
+AC_CHECK_HEADERS([linux/netlink.h netlink/netlink.h], [], [], [
 #ifdef HAVE_ASM_TYPES_H
 #include <asm/types.h>
 #endif

configure.ac

@@ -841,6 +841,9 @@
 /* Define to 1 if you have the <netinet/in.h> header file. */
 #undef HAVE_NETINET_IN_H
 
+/* Define to 1 if you have the <netlink/netlink.h> header file. */
+#undef HAVE_NETLINK_NETLINK_H
+
 /* Define to 1 if you have the <netpacket/packet.h> header file. */
 #undef HAVE_NETPACKET_PACKET_H