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/mvebu_db-88f3720_defconfig b/configs/mvebu_db-88f3720_defconfig
index caf4261..b443418 100644
--- a/configs/mvebu_db-88f3720_defconfig
+++ b/configs/mvebu_db-88f3720_defconfig
@@ -41,6 +41,7 @@
 CONFIG_ENV_IS_IN_SPI_FLASH=y
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
 CONFIG_ARP_TIMEOUT=200
+CONFIG_NET_RETRY_COUNT=50
 CONFIG_AHCI_MVEBU=y
 CONFIG_CLK=y
 CONFIG_CLK_MVEBU=y