logd: klogd crash

(cherry pick from commit a146a779)

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