There can be more than 0x20000000 swap meta blocks allocated if a swap-backed md(4) device is used. Don't panic when deallocating such a device if swap has been used.
There can be more than 0x20000000 swap meta blocks allocated if a swap-backed
md(4) device is used. Don't panic when deallocating such a device if swap
has been used.

PR:	kern/133170
Discussed with:	kib
MFC after:	3 days

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