nimble/ll: Fix calculation of connect rsp length
nimble/ll: Fix calculation of connect rsp length

This makes use of symbols to make calculations clear.

X-Original-Commit: fccddb22920e01c26079863e4a776148a3105733

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