env: Rename some other getenv()-related functions

We are now using an env_ prefix for environment functions. Rename these
other functions as well, for consistency:

   getenv_vlan()
   getenv_bootm_size()
   getenv_bootm_low()
   getenv_bootm_mapsize()
   env_get_default()

Suggested-by: Wolfgang Denk <wd@denx.de>
Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/cmd/elf.c b/cmd/elf.c
index 51dac03..5745a38 100644
--- a/cmd/elf.c
+++ b/cmd/elf.c
@@ -300,7 +300,7 @@
 				ptr += sprintf(build_buf + ptr, "e=%s", tmp);
 				tmp = env_get("netmask");
 				if (tmp) {
-					u32 mask = getenv_ip("netmask").s_addr;
+					u32 mask = env_get_ip("netmask").s_addr;
 					ptr += sprintf(build_buf + ptr,
 						       ":%08x ", ntohl(mask));
 				} else {