OS-4807 arp(1M) and ndp(1M) should use zone_get_nroot()

*** 56,65 ****
--- 56,66 ----
  #include <unistd.h>
  #include <string.h>
  #include <arpa/inet.h>
  #include <net/if_types.h>
  #include <net/if_dl.h>
+ #include <zone.h>
  
  static int file(char *);
  static int set(int, char *[]);
  static void get(char *);
  static void delete(char *);
*** 116,130 ****
                  /*
                   * the easiest way to get the complete arp table
                   * is to let netstat, which prints it as part of
                   * the MIB statistics, do it.
                   */
!                 (void) execl("/usr/bin/netstat", "netstat",
                      (n_flag ? "-np" : "-p"),
                      "-f", "inet", (char *)0);
!                 (void) fprintf(stderr, "failed to exec netstat: %s\n",
!                     strerror(errno));
                  exit(1);
  
          } else if (s_flag && (argsleft >= 2)) {
                  if (set(argsleft, &argv[optind]) != 0)
                          exit(1);
--- 117,135 ----
                  /*
                   * the easiest way to get the complete arp table
                   * is to let netstat, which prints it as part of
                   * the MIB statistics, do it.
                   */
!                 char netstat_path[MAXPATHLEN];
!                 const char *zroot = zone_get_nroot();
!                 (void) snprintf(netstat_path, sizeof (netstat_path), "%s%s", zroot != NULL ?
!                     zroot : "", "/usr/bin/netstat");
!                 (void) execl(netstat_path, "netstat",
                      (n_flag ? "-np" : "-p"),
                      "-f", "inet", (char *)0);
!                 (void) fprintf(stderr, "failed to exec %s: %s\n",
!                     netstat_path, strerror(errno));
                  exit(1);
  
          } else if (s_flag && (argsleft >= 2)) {
                  if (set(argsleft, &argv[optind]) != 0)
                          exit(1);