Staging: batman-adv: avoid having the same error message more than once

The routing code has 2 sections which warn about ttl exceeded. The
corresponding warnings were identical which makes it hard to debug. In
addition, batman-adv does not need to warn about ttl exceeded in case
we encountered an echo request as this is commonly used to generate
traceroute graphs.

Signed-off-by: Marek Lindner <lindner_marek@yahoo.de>
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>