Shorten local name in EIR data according to UTF encoding rules

Use case:
Test short name after setting the name with maximum length

Steps to reproduce:
1) Phone A: Rename bluetooth into a 60 character Chinese name
2) Phone B: Discover phone A.
3) The short name of phone A will display in phone B and the short
name cantains unrecognizable chars.

Root cause:
As Chinese characters are encoded in different
length in UTF, if shorten BT name in fixed length,
there will be unrecognized characters

Fix:
Shorten BT name according to UTF encoding rule and decrease
the length.

Change-Id: I5f1e49c1b5d87d5e220538c90e297c50ccc790ff