fix(lwip): fix build error with PPP enabled #3812

Job	Run time
A9-rtsmart :kernel/kernel_basic.cfg	6m 28s
RISCV-rtsmart :default.cfg	1m 5s
AARCH64-rtsmart :default.cfg	1m 15s
AARCH64-smp :default.cfg	1m 28s
A9-smp :default.cfg	1m 57s
A9 :kernel/kernel_basic.cfg	6m 35s
AARCH64 :default.cfg	1m 22s
A9-rtsmart :kernel/mem.cfg	1m 16s
A9 :default.cfg	1m 30s
A9-smp :kernel/kernel_basic.cfg	6m 50s
RISCV :default.cfg	1m 6s
A9 :kernel/ipc.cfg	5m 12s
A9-smp :kernel/ipc.cfg	5m 31s
XUANTIE-rtsmart :kernel/mem.cfg	2m 10s
RISCV-smp :default.cfg	1m 33s
RISCV :kernel/ipc.cfg	5m 4s
XUANTIE-rtsmart :kernel/kernel_basic.cfg	7m 14s
RISCV :kernel/kernel_basic.cfg	6m 34s
RISCV-rtsmart :kernel/ipc.cfg	5m 37s
A9 :kernel/mem.cfg	1m 29s
A9-smp :kernel/mem.cfg	1m 41s
XUANTIE-rtsmart :default.cfg	1m 50s
RISCV-rtsmart :kernel/kernel_basic.cfg	6m 49s
RISCV :kernel/mem.cfg	1m 8s
A9 :cpp11/cpp11.cfg	1m 20s
A9 :components/lwip.cfg	1m 37s
A9 :kernel/atomic_c11.cfg	1m 19s
A9 :components/netdev.cfg	1m 34s
A9-rtsmart :default.cfg	1m 12s
A9 :components/sal.cfg	1m 30s
A9 :components/dfs.cfg	1m 21s
XUANTIE-rtsmart :kernel/ipc.cfg	6m 10s
RISCV-rtsmart :kernel/mem.cfg	1m 16s
RISCV-smp :kernel/mem.cfg	1m 33s
AARCH64-rtsmart :kernel/mem.cfg	1m 21s
AARCH64-smp :kernel/mem.cfg	1m 20s
AARCH64 :kernel/mem.cfg	1m 17s
RISCV :kernel/atomic_c11.cfg	1m 38s
A9-rtsmart :kernel/ipc.cfg	5m 28s
	1h 52m 40s

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