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/snapper9g20_defconfig b/configs/snapper9g20_defconfig
index eb62cfd..4ed958d 100644
--- a/configs/snapper9g20_defconfig
+++ b/configs/snapper9g20_defconfig
@@ -34,6 +34,7 @@
 CONFIG_ENV_OVERWRITE=y
 CONFIG_ENV_IS_IN_NAND=y
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
+CONFIG_NET_RETRY_COUNT=20
 CONFIG_TFTP_TSIZE=y
 CONFIG_AT91_GPIO=y
 CONFIG_CMD_PCA953X=y