net: apps: Ignore multicast context get fails in echo-server

The echo-server should work just fine even if the multicast
context cannot be get. By default there are only two contexts
so the multicast would fail always anyway and the program
would not run properly.

Change-Id: Ia9737cbda4a933a208aae020f055f0b6062b4f47
Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>