logd: klogd crash

dmesg parser could wrap taglen limit resulting in out of bound
accesses. Can lead to crash or data corruption.

Fixed an issue with two-word tag parsing. Switched to case
insensitive tag content matching. Added a few extra limit
checks that could also wrap, simplified the parsing, then added
means to stop using hard coded constants.

Bug: 30688716
Bug: 30050636
Bug: 30614675
Bug: 25620123
Change-Id: Iae4f664f63ef7b842d82eaa1638b6d7a0d28fd18