netlabel: Fix memory leak in netlbl_mgmt_add_common

Hulk Robot reported memory leak in netlbl_mgmt_add_common.
The problem is non-freed map in case of netlbl_domhsh_add() failed.

BUG: memory leak
unreferenced object 0xffff888100ab7080 (size 96):
  comm "syz-executor537", pid 360, jiffies 4294862456 (age 22.678s)
  hex dump (first 32 bytes):
    05 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
    fe 00 00 00 00 00 00 00 00 00 00 00 00 00 00 01  ................
  backtrace:
    [<0000000008b40026>] netlbl_mgmt_add_common.isra.0+0xb2a/0x1b40
    [<000000003be10950>] netlbl_mgmt_add+0x271/0x3c0
    [<00000000c70487ed>] genl_family_rcv_msg_doit.isra.0+0x20e/0x320
    [<000000001f2ff614>] genl_rcv_msg+0x2bf/0x4f0
    [<0000000089045792>] netlink_rcv_skb+0x134/0x3d0
    [<0000000020e96fdd>] genl_rcv+0x24/0x40
    [<0000000042810c66>] netlink_unicast+0x4a0/0x6a0
    [<000000002e1659f0>] netlink_sendmsg+0x789/0xc70
    [<000000006e43415f>] sock_sendmsg+0x139/0x170
    [<00000000680a73d7>] ____sys_sendmsg+0x658/0x7d0
    [<0000000065cbb8af>] ___sys_sendmsg+0xf8/0x170
    [<0000000019932b6c>] __sys_sendmsg+0xd3/0x190
    [<00000000643ac172>] do_syscall_64+0x37/0x90
    [<000000009b79d6dc>] entry_SYSCALL_64_after_hwframe+0x44/0xae

Fixes: 63c41688 ("netlabel: Add network address selectors to the NetLabel/LSM domain mapping")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Liu Shixin <liushixin2@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>