nimble/ll: Verify length of Terminate Ind
nimble/ll: Verify length of Terminate Ind

Make sure Terminate ind has correct len. Otherwise do not procced but
reply with LL_UNKNOWN_RSP

This should fix LL/PAC/SLA/BI-01 and LL/PAC/MAS/BI-01

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