Check remote LMP version before enabling secure connections

Request remote version information for LE links when connecting and
ensure LMP version is >= 8 (Bluetooth 4.2) before setting the LinkKey
bits in the pairing request.

This is to ensure older remote devices do not get confused by the
additional bit(s) in the pairing request.

Bug: 25277879
Change-Id: I25424e541fa5244d8f522dffc62cdedc24f4f35b