net: nfs: make NFS_TIMEOUT configurable

NFS_TIMEOUT is constant value defined in net/nfs.c. But sometimes it needs to adjust.
This patch enables to override NFS_TIMEOUT by defining CONFIG_NFS_TIMEOUT in a board specific config file.

Signed-off-by: Tetsuyuki Kobayashi <koba@kmckk.co.jp>
diff --git a/net/nfs.c b/net/nfs.c
index 5b99763..7f2393f 100644
--- a/net/nfs.c
+++ b/net/nfs.c
@@ -31,7 +31,11 @@
 
 #define HASHES_PER_LINE 65	/* Number of "loading" hashes per line	*/
 #define NFS_RETRY_COUNT 30
-#define NFS_TIMEOUT 2000UL
+#ifndef CONFIG_NFS_TIMEOUT
+# define NFS_TIMEOUT 2000UL
+#else
+# define NFS_TIMEOUT CONFIG_NFS_TIMEOUT
+#endif
 
 static int fs_mounted;
 static unsigned long rpc_id;