samples: net: echo-client: Increase buf count for frdm-k64f

Increasing the network buffer count for frdm-k64f so that the
device will not run out of memory so easily.

Fixes zephyrproject-rtos#7678

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

samples/net/echo_client/prj_frdm_k64f.conf

@@ -8,10 +8,10 @@ CONFIG_NET_UDP=y
 CONFIG_NET_TCP=y
 CONFIG_NET_STATISTICS=y
 
-CONFIG_NET_PKT_RX_COUNT=14
-CONFIG_NET_PKT_TX_COUNT=14
-CONFIG_NET_BUF_RX_COUNT=30
-CONFIG_NET_BUF_TX_COUNT=30
+CONFIG_NET_PKT_RX_COUNT=50
+CONFIG_NET_PKT_TX_COUNT=50
+CONFIG_NET_BUF_RX_COUNT=50
+CONFIG_NET_BUF_TX_COUNT=50
 CONFIG_NET_IF_UNICAST_IPV6_ADDR_COUNT=5
 CONFIG_NET_IF_MCAST_IPV6_ADDR_COUNT=5
 CONFIG_NET_IF_UNICAST_IPV4_ADDR_COUNT=1