Convert CONFIG_NET_RETRY_COUNT to Kconfig

This converts the following to Kconfig:
   CONFIG_NET_RETRY_COUNT

Cc: Ramon Fried <rfried.dev@gmail.com>
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/etamin_defconfig b/configs/etamin_defconfig
index 15a43e7..32800ec 100644
--- a/configs/etamin_defconfig
+++ b/configs/etamin_defconfig
@@ -72,6 +72,7 @@
 CONFIG_ENV_IS_IN_NAND=y
 CONFIG_SYS_REDUNDAND_ENVIRONMENT=y
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
+CONFIG_NET_RETRY_COUNT=10
 CONFIG_BOOTP_SEND_HOSTNAME=y
 CONFIG_SPL_DM=y
 # CONFIG_SPL_BLK is not set