Remove {GETSOCKNAME,GETPEERNAME}_ARG2_TYPE

Remove {GETSOCKNAME,GETPEERNAME}_ARG2_TYPE

We have had code since at least 1.6 in changepw.c and sendto_kdc.c
which assumes that we can pass a struct sockaddr * as the second
argument to getsockname() and getpeername(), so we can safely get rid
of that configure logic.  Also fix potential alignment issues in
krb5_sendauth() by using a struct sockaddr_storage instead of a
1024-byte character buffer to hold the local and peer addresses.

[ghudson@mit.edu: adjusted style of new code slightly; rewrote commit
message]