env: Rename setenv() to env_set()

We are now using an env_ prefix for environment functions. Rename setenv()
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/drivers/net/sandbox-raw.c b/drivers/net/sandbox-raw.c
index f5fa0e8..590ae0c 100644
--- a/drivers/net/sandbox-raw.c
+++ b/drivers/net/sandbox-raw.c
@@ -33,8 +33,8 @@
 
 	if (strcmp(interface, "lo") == 0) {
 		priv->local = 1;
-		setenv("ipaddr", "127.0.0.1");
-		setenv("serverip", "127.0.0.1");
+		env_set("ipaddr", "127.0.0.1");
+		env_set("serverip", "127.0.0.1");
 	}
 	return sandbox_eth_raw_os_start(interface, pdata->enetaddr, priv);
 }