host/gap: fix doxygen for ble_gap_ext_disc()
host/gap: fix doxygen for ble_gap_ext_disc()

Documentation for the parameters `filter_duplicates` and
`filter_policy` for ble_gap_ext_disc() was missing.

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