POSIX requires <limits.h> for PATH_MAX and NAME_MAX

Author: Anthony G. Basile <blueness@gentoo.org>

diff -Naur net-snmp-5.7.3.orig/agent/mibgroup/util_funcs/get_pid_from_inode.c net-snmp-5.7.3/agent/mibgroup/util_funcs/get_pid_from_inode.c
--- net-snmp-5.7.3.orig/agent/mibgroup/util_funcs/get_pid_from_inode.c	2014-12-08 15:23:22.000000000 -0500
+++ net-snmp-5.7.3/agent/mibgroup/util_funcs/get_pid_from_inode.c	2018-02-21 15:34:06.237028136 -0500
@@ -6,6 +6,7 @@
 
 #include <ctype.h>
 #include <stdio.h>
+#include <limits.h>
 #if HAVE_STDLIB_H
 #include <stdlib.h>
 #endif