Wifi patcher: Support multiple firmware types

Refactor the H3 wifi address patching utility to work with
more than one firmware type at the same time. Add support
for patching the H3+B wifi firmware from update v1.04.

Signed-off-by: evilwombat <evilwombat@server.fake>
fwparser/fwunpacker: Ignore sections with invalid length

Skip a section if its length claims to be negative
(invalid). This can happen if the section magic occurs in
any executable code at the start of the update file, before
we get to the actual section headers.

Signed-off-by: evilwombat <evilwombat@server.fake>