Make StaticHeader::sigblock_to_buf private
Make StaticHeader::sigblock_to_buf private

It is only used within the module, so it can be made private to the module.

Signed-off-by: mulhern <7b51bcf507bcd7afb72bf8663752c0ddbeb517f6@redhat.com>

stratis-storage/stratisd,stratis-storage/stratisd,stratis-storage/stratisd,trgill/stratisd,mulkieran/stratisd,mulkieran/stratisd,trgill/stratisd