DLPX-84445 Generate BTF for our custom zfs and spl kernel modules

[prakashsurya]

Problem

When building the ZFS kernel modules, we don't generate BTF due to missing the "vmlinux" at the location expected by the kernel module build system.

Solution

The solution taken in this PR is to install the "dbgsym" kernel packages which install the "vmlinux" file, and then also add the symlink to that file at the location the kernel module build system expects.

Testing Done

• git-ab-pre-push -b zfs is here

• With this change, on ESX:

$ sudo bpftrace -v /opt/delphix/server/bin/nfs_delete.trace
INFO: node count: 111
Attaching 5 probes...

Program ID: 135

The verifier log:
processed 50 insns (limit 1000000) max_states_per_insn 0 total_states 3 peak_states 3 mark_read 1

Attaching kretfunc:nfsd:nfsd_unlink

Program ID: 136

The verifier log:
processed 2 insns (limit 1000000) max_states_per_insn 0 total_states 0 peak_states 0 mark_read 0

Attaching kfunc:zfs:zfs_ioc_pool_destroy

Program ID: 137

The verifier log:
processed 467 insns (limit 1000000) max_states_per_insn 0 total_states 11 peak_states 11 mark_read 7

Attaching kfunc:vmlinux:vfs_unlink

Program ID: 138

The verifier log:
processed 100 insns (limit 1000000) max_states_per_insn 0 total_states 6 peak_states 6 mark_read 2

Attaching kfunc:nfsd:nfsd_unlink

[tperkins-perforce]

lgtm

[david-mendez1]

Looks good, waiting for the ab-pre-push test...