various files - fix some alerts raised by lgtm code analysis

This patch fixes several issues reported by the lgtm code analysis tool:

https://lgtm.com/projects/g/asterisk/asterisk

Not all reported issues were addressed in this patch. This patch mostly fixes
confirmed reported errors, potential problematic code points, and a few other
"low hanging" warnings or recommendations found in core supported modules.
These include, but are not limited to the following:

* innapropriate stack allocation in loops
* buffer overflows
* variable declaration "hiding" another variable declaration
* comparisons results that are always the same
* ambiguously signed bit-field members
* missing header guards

Change-Id: Id4a881686605d26c94ab5409bc70fcc21efacc25

codecs/ex_g722.h

@@ -7,6 +7,9 @@
  *
  */
 
+#ifndef ASTERISK_EX_G722_H
+#define ASTERISK_EX_G722_H
+
 static uint8_t ex_g722[] = {
 	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
 	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
@@ -46,3 +49,5 @@ static struct ast_frame *g722_sample(void)
 
 	return &f;
 }
+
+#endif /* ASTERISK_EX_G722_H */