struct amr_header: copy comments to little endian part

I will soon apply struct_endianess.py to this code, and then the comments that
are now only in the big endian part would be lost. Copy them to preserve them.

Change-Id: Ie4279928bd77a5d425d0e7a3c4d58bac3cf0230a

include/osmocom/netif/amr.h

@@ -55,12 +55,12 @@ struct amr_hdr {
 #elif OSMO_IS_LITTLE_ENDIAN
 	/* Payload Header */
 	uint8_t pad1:4,
-		cmr:4;
+		cmr:4;	/* Codec Mode Request */
 	/* Table of Contents */
 	uint8_t pad2:2,
-		q:1,
-		ft:4,
-		f:1;
+		q:1,	/* OK (not damaged) at origin? */
+		ft:4,	/* coding mode */
+		f:1;	/* followed by another speech frame? */
 #endif
 } __attribute__((packed));