samples: net: Add echo_client build test for frdm CC2520 configuration

Add build test to sanity_check to get a complex net app being built
for frdm-k64f.

Change-Id: Ib136f7964b65ad2167a3ed4484bff3bfe2a7ebad
Signed-off-by: Andrei Emeltchenko <[email protected]>

Author: finikorg

samples/net/echo_client/testcase.ini

@@ -12,3 +12,9 @@ extra_args = CONF_FILE="prj_bt.conf"
 arch_whitelist = x86
 platform_whitelist = minnowboard
 skip = true
+
+[test_net]
+tags = net
+build_only = true
+extra_args = CONF_FILE="prj_frdm_k64f_cc2520.conf"
+platform_whitelist = frdm_k64f