nimble/gap: Fix for checking sc only mode
nimble/gap: Fix for checking sc only mode

When host is configure for SC only mode, make sure to reject pairing
when remote wants Legacy pairing.

This fixes GAP/SEC/SEM/BV-23-C and GAP/SEC/SEM/BV-24-C

apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble