Fix dangling arch pointer in gen_bpf

[virajmalia]

Problem

I ran a cppcheck scan on the repository and found 2 instances of state->arch = &pseudo_arch that are not reset before 6 return paths:

<error id="autoVariables" severity="error" msg="Address of local auto-variable assigned to a function parameter." verbose="Dangerous assignment - the function parameter is assigned the address of a local auto-variable. Local auto-variables are reserved from the stack which is freed when the function ends. So the pointer to a local variable is invalid after the function ends." cwe="562">
    <location file="/workspace/src/gen_bpf.c" line="2029" column="2"/>
</error>
<error id="autoVariables" severity="error" msg="Address of local auto-variable assigned to a function parameter." verbose="Dangerous assignment - the function parameter is assigned the address of a local auto-variable. Local auto-variables are reserved from the stack which is freed when the function ends. So the pointer to a local variable is invalid after the function ends." cwe="562">
    <location file="/workspace/src/gen_bpf.c" line="2102" column="2"/>
</error>

state->arch has a longer lifetime than pseudo_arch and the function _gen_bpf_build_bpf returns without resetting state->arch.

Fix

• Set state->arch = NULL before the return statements

Why?

• Although there are no use-after-free instances that I could find, future code modifications may not be verifying that, so it makes sense to keep the code clean and avoid future problems.

Verification

• Build and tests passed locally