Provide more suitable API to query acl role

Add: stack/acl/btm_acl.cc::acl_is_role_master()
to:
stack/gatt/gatt_db.cc::gatts_db_read_attr_value_by_type()

Working towards encapsulation of tACL_CONN

Bug: 159815595
Tag: #refactor
Test: compile & verify basic functions working
Change-Id: I2462c1bde4e91fe5daec4031362755cd75a91fa5