env: Rename common functions related to setenv()

We are now using an env_ prefix for environment functions. Rename these
commonly used functions, for consistency. Also add function comments in
common.h.

Suggested-by: Wolfgang Denk <wd@denx.de>
Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/net/net.c b/net/net.c
index 2268890..be33c66 100644
--- a/net/net.c
+++ b/net/net.c
@@ -616,8 +616,8 @@
 			if (net_boot_file_size > 0) {
 				printf("Bytes transferred = %d (%x hex)\n",
 				       net_boot_file_size, net_boot_file_size);
-				setenv_hex("filesize", net_boot_file_size);
-				setenv_hex("fileaddr", load_addr);
+				env_set_hex("filesize", net_boot_file_size);
+				env_set_hex("fileaddr", load_addr);
 			}
 			if (protocol != NETCONS)
 				eth_halt();