Make ifupdown2 print meaningful error when interface name length exceeds 15 characters

Ticket: CM-5882
Reviewed By: gospo
Testing Done: unit tested

When a user enters an interface name longer than 15 characters,
the error message is not clear about what the problem is.

   warning: netlink: Numerical result out of range <<<<<<<<<<<<<<<<

This patch catches the error before netlink gets the call and
prints

    error: the following interface names are too long: bond-xconnect.1006

ifupdown/utils.py

@@ -49,4 +49,12 @@ class utils():
                 ifacenames.append('%s-%d' %(iface_range[0], i))
         return ifacenames
 
+    @classmethod
+    def check_ifname_size_invalid(cls, name=''):
+        """ IFNAMSIZ in include/linux/if.h is 16 so we check this """
+        IFNAMSIZ = 16
+        if len(name) > IFNAMSIZ - 1:
+            return True
+        else:
+            return False