Add null check for tupleOrig in ConntrackMessage

ConntrackSocketTest#testIpv4ConntrackSocket always fail in cuttlefish
because it gets NullPointerException when accessing tupleOrig in
ConntrackMessage. tupleOrig can be null if it doesn't have source IP.

This situation happens when dumping the following conntrack entry:
vsoc_x86_64:/ # cat /proc/net/nf_conntrack
ipv4     2 unknown  2 570 src=0.0.0.0 dst=224.0.0.22 [UNREPLIED] \
src=224.0.0.22 dst=0.0.0.0 mark=0 secctx=u:object_r:unlabeled:s0 use=2

Bug: 280203901
Test: atest TetheringPrivilegedTests (on cuttlefish)
Change-Id: Iddc8cb390a4369190d535f4694e0e5fa4b6e590f
1 file changed