nimble/ll: Fix adv data length calculation if SyncInfo is present
nimble/ll: Fix adv data length calculation if SyncInfo is present

When placing SyncInfo into Extended Header it needs to be taken into
account when calculating available space for advertisign data.

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