BGP: Add support for BGP hostname capability

This is an implementation of draft-walton-bgp-hostname-capability-02.
It is implemented since quite some time for FRR and in datacenter, this
gives a nice output to avoid using IP addresses.

It is disabled by default. The hostname is retrieved from uname(2) and
can be overriden with "hostname" option. The domain name is never set
nor displayed.

Minor changes by committer.

sysdep/unix/main.c

@@ -20,6 +20,7 @@
 #include <pwd.h>
 #include <grp.h>
 #include <sys/stat.h>
+#include <sys/utsname.h>
 #include <libgen.h>
 
 #include "nest/bird.h"
@@ -88,6 +89,21 @@ drop_gid(gid_t gid)
     die("setgroups: %m");
 }
 
+/*
+ *	Hostname
+ */
+
+char *
+get_hostname(linpool *lp)
+{
+  struct utsname uts = {};
+
+  if (uname(&uts) < 0)
+      return NULL;
+
+  return lp_strdup(lp, uts.nodename);
+}
+
 /*
  *	Reading the Configuration
  */

sysdep/unix/unix.h

@@ -24,6 +24,7 @@ extern int parse_and_exit;
 void async_config(void);
 void async_dump(void);
 void async_shutdown(void);
+char *get_hostname(linpool *lp);
 void cmd_check_config(const char *name);
 void cmd_reconfig(const char *name, int type, uint timeout);
 void cmd_reconfig_confirm(void);