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/turris_omnia_defconfig b/configs/turris_omnia_defconfig
index a9d840e..ec9f766 100644
--- a/configs/turris_omnia_defconfig
+++ b/configs/turris_omnia_defconfig
@@ -63,6 +63,7 @@
 CONFIG_ENV_OVERWRITE=y
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
 CONFIG_ARP_TIMEOUT=200
+CONFIG_NET_RETRY_COUNT=50
 CONFIG_SPL_OF_TRANSLATE=y
 CONFIG_AHCI_PCI=y
 CONFIG_AHCI_MVEBU=y