bpf: Return proper address for non-zero offsets in insn array

In the Linux kernel, the following vulnerability has been resolved: bpf: Return proper address for non-zero offsets in insn array The map_direct_value_addr() function of the instruction array map incorrectly adds offset to the resulting address. This is a bug, because later the resolve_pseudo_ldimm64() function adds the offset. Fix it. Corresponding selftests are added in a consequent commit.