util: fix uninitialized table

util: fix uninitialized table

Most of the 256 values in the 'generic_to_slot' table were supposed to
be initialized with the default value 0xff, but were left at zero
(from CALLOC_STRUCT()) instead.

Noticed by clang:

u_linkage.h:60:31: warning: argument to 'sizeof' in 'memset' call is the same expression as the destination;
      did you mean to provide an explicit length? [-Wsizeof-pointer-memaccess]
   memset(table, 0xff, sizeof(table));
          ~~~~~               ^~~~~

Also fix a signed/unsigned comparison and a comment typo here.

NOTE: This is a candidate for the 8.0 branch.

Reviewed-by: Brian Paul <brianp@vmware.com>