net/ucx: Fix FreeBSD runtime portability issues
Adjust several Linux-specific runtime assumptions in UCX for FreeBSD:
- use FreeBSD-specific network interface handling where Linux sysfs logic is not available
- avoid Linux-only IPOIB and bridge detection paths
- improve pthread_create() error reporting
- provide FreeBSD fallbacks for memory remapping and affinity helpers
This fixes multiple runtime failures and device discovery issues on FreeBSD.
PR: 293867
Sponsored by: UNIS Labs
MFH: 2026Q2