misc: Doxygen tweaks: fixed some typos and minor errors

Doxygen generates quite a lot of warnings on libosmocore. Some of them
are obvious typos - this patch aims to fix such low-hanging fruit.
diff --git a/src/bitvec.c b/src/bitvec.c
index 714c11b..8da5a48 100644
--- a/src/bitvec.c
+++ b/src/bitvec.c
@@ -132,7 +132,7 @@
 
 /*! \brief set a bit at given position in a bit vector
  *  \param[in] bv bit vector on which to operate
- *  \param[in] bitnum number of bit to be set
+ *  \param[in] bitnr number of bit to be set
  *  \param[in] bit value to which the bit is to be set
  */
 int bitvec_set_bit_pos(struct bitvec *bv, unsigned int bitnr,