APF: do not drop packets with hop-by-hop options

The current APF code looks at the IPv6 next-header field to make a pass
/ drop decision based on the contained protocol.
Since MLD packets set the router-alert hop-by-hop option (next-header
type 0), they have been dropped inadvertently as "generic multicast
traffic".

We should consider being a bit smarter about only letting MLD packets
pass, but since HBH options are rarely used, this patch might just be
"good enough".

Test: TH
Bug: 149630944
Change-Id: I84e7d8777d6bf78c0ea4b449f2f0fd47e1266309
1 file changed