net/ucx: Fix FreeBSD UCM relocation handling

On FreeBSD, dynamic-section pointers observed through dl_iterate_phdr()
for shared objects need to be rebased by dlpi_addr before dereference.

Also fix the PT_LOAD end range calculation to include the object base
address when tracking the library address span.

This fixes runtime failures in UCM relocation patching on FreeBSD.

PR: 293867
Sponsored by: UNIS Labs
MFH: 2026Q2