dumpstate: close socket after accepting

Close socket just after accept(), to make sure that connect() by client
will get error when the socket is used by the other services.

Bug: 135575100
Test: execute bugreport in parallel

Change-Id: I4e8a46e41519fa97cf41dde8955cf37361c6fa99
Signed-off-by: Kansho Nishida <kansho@google.com>