Revert "4384. [bug] isc_buffer_reallocate returns wrong result when passed"

This reverts commit 01a0206c.

CHANGES

-4384.	[bug]		isc_buffer_reallocate returns wrong result when passed
-			a smaller length than what is already allocated.
-			[RT #42612]
-
 4383.	[bug]		Correct spelling error in stats channel description of
 			"EDNS client subnet option received". [RT #42633]
 

lib/isc/buffer.c

@@ -523,7 +523,7 @@ isc_buffer_reallocate(isc_buffer_t **dynbuffer, unsigned int length) {
 	REQUIRE((*dynbuffer)->mctx != NULL);
 
 	if ((*dynbuffer)->length > length)
-		return (ISC_R_SUCCESS);
+		return (ISC_R_NOSPACE);
 
 	/*
 	 * XXXMUKS: This is far more expensive than plain realloc() as