Reset key-generation parameters for each enctype

In add_key_pwd, initialize s2k_params to NULL inside the loop over
enctypes instead of outside the loop, so that if the afs3 salt type
is used it does not contaminate later enctype/salt pairs in the list.

(cherry picked from commit 381cf01afb13ad28de0927de37f8e1d12749bf49)

https://github.com/krb5/krb5/commit/4abb885838676107ef5dd86c283c04ba5a1351d0
Author: Ben Kaduk <kaduk@mit.edu>
Committer: Tom Yu <tlyu@mit.edu>
Commit: 4abb885838676107ef5dd86c283c04ba5a1351d0
Branch: krb5-1.11
 src/lib/kdb/kdb_cpw.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)