pmdabcc: strict BCC cachestat compatibility for metric types
pmdabcc: strict BCC cachestat compatibility for metric types

buffers/cached are MBs in BCC cachestat, use the same semantics
in BCC PMDA module as well.

adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp