mesh: Fix initializing connection handle for PB GATT
mesh: Fix initializing connection handle for PB GATT

Commit bf1ff83361edd5494637cac69b61a6bb228f9870 introduced a regression
due to not initialized conn handle. Provisioning code would use
GATT bearer even though there was no active connection.

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