Fix bug with resolving relative symlinks during linux header detection

[ddelnano]

Summary: Fix bug with resolving relative symlinks during linux header detection

Please see linked issue for details

Relevant Issues: Closes #2037

Type of change: /kind bugfix

Test Plan: Verified the following

• Confirmed with user that reported the issue that this works for openSUSE's MicroOS linux headers
• Verified on Ubuntu that using an absolute symlink works (upstream package, no modification)

ddelnano@dev-vm:/lib/modules/6.8.0-1015-gcp$ ls -l build
lrwxrwxrwx 1 root root 37 Sep  2 14:42 build -> /usr/src/linux-headers-6.8.0-1015-gcp

# Verify custom built stirling_wrapper identifies absolute headers
$ sudo docker run -v /:/host -v /sys:/sys -v /var/lib/docker:/var/lib/docker --pid=host --cgroupns host --env "PL_HOST_PATH=/host"  bazel/src/stirling/binaries:stirling_wrapper_image

I20241011 21:32:38.893605 395713 linux_headers.cc:257] Looking for host Linux headers at /host/lib/modules/6.8.0-1015-gcp/build.
I20241011 21:32:38.893646 395713 linux_headers.cc:237] Symlink target is an absolute path. Converting that to host path: /usr/src/linux-headers-6.8.0-1015-gcp -> /host/usr/src/linux-headers-6.8.0-1015-gcp.
I20241011 21:32:38.893750 395713 linux_headers.cc:261] Linked host headers at /host/usr/src/linux-headers-6.8.0-1015-gcp to symlink in pem namespace at /lib/modules/6.8.0-1015-gcp/build.
I20241011 21:32:38.893783 395713 linux_headers.cc:257] Looking for host Linux headers at /host/lib/modules/6.8.0-1015-gcp/source.

• Verified on Ubuntu that using a relative symlink (modified by hand with reproduction steps in Upstream kernel header packages with relative symlinks always fall back to Pixie prepackaged headers  #2037)

# Verify build is a relative symlink and resolves outside a container
ddelnano@dev-vm:/lib/modules/6.8.0-1015-gcp$ ls -l
total 1480
lrwxrwxrwx  1 root root     48 Oct 11 20:39 build -> ../../../../usr/src/linux-headers-6.8.0-1015-gcp

# Verify custom built stirling_wrapper identifies relative headers
$ sudo docker run -v /:/host -v /sys:/sys -v /var/lib/docker:/var/lib/docker --pid=host --cgroupns host --env "PL_HOST_PATH=/host"  bazel/src/stirling/binaries:stirling_wrapper_image

I20241011 21:30:16.825937 395471 linux_headers.cc:257] Looking for host Linux headers at /host/lib/modules/6.8.0-1015-gcp/build.
I20241011 21:30:16.825973 395471 linux_headers.cc:242] Symlink target is a relative path. Concatenating it to parent directory: /host/lib/modules/6.8.0-1015-gcp/../../../../usr/src/linux-headers-6.8.0-1015-gcp
I20241011 21:30:16.826067 395471 linux_headers.cc:261] Linked host headers at /host/lib/modules/6.8.0-1015-gcp/../../../../usr/src/linux-headers-6.8.0-1015-gcp to symlink in pem namespace at /lib/modules/6.8.0-1015-gcp/build.

Changelog Message: Fixed an issue where certain linux upstream distro's header packages would fail to be identified

[feynmanliang]

Thank you!