MFC r179097:

• Assert that we don't send new provider event for a provider which has G_PF_WITHER flag set.
• Fix typo in assertion condition (sorry, but I forgot who report that).

MFC r179151:
Force commit to note, that the typo in KASSERT() was:

PR: kern/116896
Reported by: VANHULLEBUS Yvan <vanhu@netasq.com>