lib/inet6.c:INET6_rresolve() - various fixes

1) Fall-back to numeric address if getnameinfo fails.
   Reverse lookup is not mandatory, therefore its fail
   is not an error. Just return numeric address in that case.
   This makes netstat/route show IPv6 address instead of
   [UNKNOWN] in case of DNS problems.

2) Pass length of 'name' buffer into function.
   'name' is a pointer and therefore sizeof(name)
   returns size of pointer and not size of the buffer.
   see http://stackoverflow.com/questions/14298710/c-pointers-and-arrays-sizeof-operator
   The sizeof() usage was added with commit 604785adc,
   so I checked all the other changes in that commit
   and they seem to be OK.

3) remove unused 's' variable
rprint_fib6() was passing 1 instead of 'numeric' into INET6_sprint()