bitvec: correct comment in bitvec_alloc

The function allocates x bytes not bits for the vector.

Change-Id: I60fbe9fe9acd11c5d3232207f1bb677e8a98625f
diff --git a/src/bitvec.c b/src/bitvec.c
index 0f56e3e..dac0401 100644
--- a/src/bitvec.c
+++ b/src/bitvec.c
@@ -401,7 +401,7 @@
 }
 
 /*! Allocate a bit vector
- *  \param[in] size Number of bits in the vector
+ *  \param[in] size Number of bytes in the vector
  *  \param[in] ctx Context from which to allocate
  *  \return pointer to allocated vector; NULL in case of error */
 struct bitvec *bitvec_alloc(unsigned int size, TALLOC_CTX *ctx)