Update oes_api_fdb.h

Change return code descriptions in several functions.
Change prototype of  oes_api_fdb_uc_mac_addr_set - In case the operation failed on one entry (or more), an error will be returned, mac_entry_list_p will store those entries, and their quantity
ill be stored in mac_cnt.
Merge pull request #6 from eyalkeren/patch-2

Update oes_api_fdb.h