transport: propagate fsck configuration during bundle fetch

transport: propagate fsck configuration during bundle fetch

When fetching directly from a bundle, fsck message severity
configuration is not propagated to the underlying git-index-pack(1). It
is only capable of enabling or disabling fsck checks entirely. This does
not align with the fsck behavior for fetches through git-fetch-pack(1).

Use the fsck config parsing from fetch-pack to populate fsck message
severity configuration and wire it through to `unbundle()` to enable the
same fsck verification as done through fetch-pack.

Signed-off-by: Justin Tobler <jltobler@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>