MFC r345051 (by imp): Add -l to camcontrol readcap.

The -l flag sends only the READ CAPACITY (16) sevice action. Normally
we send the READ CAPACITY (10) command, and only send RC16 when the
capacity is larger than 2TB (since that's the max RC10 can
report). However, some badly programmed drives report different
numbers for RC10 and RC16. This can be hard to diagnose, but generally
there's a "Logical block address out of range" error when RC16 reports
a larger number than RC10 and the RC10 number is the correct one. By
comparing the output of readcap with and without the -l argmuent, one
can determine if there's a mismatch and if the DA_Q_NO_RC16 quirk is
needed.