Fix what looks like a cut-and-paste error in our read_negTokenInit() function.

Fix what looks like a cut-and-paste error in our read_negTokenInit() function.

We should never be calling asn1_push_XXX functions inside an asn1
reading function. Change asn1_push_tag() -> asn1_start_tag() and
asn1_pop_tag() -> asn1_end_tag(). This allows us to connect to a
NetApp filer at the Microsoft plugfest.

Andrew PLEASE CHECK !

Jeremy.

Fix bug #7449 (spnego data mis-parsed - returns incorrect mechListMIC string).
(cherry picked from commit 70098b751c10e632738f687976e6ef5e5fb2fc7b)