sw64: bpf: fix insn_offset

Sunway inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I5PNHA



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Since ctx->idx is the index of the next jited instruction, value of
insn_offset should be set before build_insn().

Allocate 1 more entry for insn_offset[], and give epilogue_offset to
it, so the correct jump offset can be calculated if the last
instruction is BPF_JMP.

Signed-off-by: Mao Minkai <maominkai@wxiat.com>
Signed-off-by: Gu Zitao <guzitao@wxiat.com>