bgpd, isisd, ospfd: coverity fixes

[ashred-lnx]

ospfd/ospf_ext.c - buffer overflow
bgpd/bgp.c - ignore Coverity
isisd/isis.c - Ensure packet is at least LLC_LEN bytes to prevent underflow

[greptile-apps]

Greptile Summary

This PR addresses three Coverity static analysis warnings across the BGP, IS-IS, and OSPF subsystems.

Key changes:

• bgpd/bgpd.c: Added coverity[leaked_storage] annotations to suppress false positive memory leak warnings. The memory is correctly managed through the clearing batch lifecycle and freed by bgp_clearing_batch_completed().
• isisd/isis_pfpacket.c: Fixed a critical buffer underflow vulnerability by validating that bytesread >= LLC_LEN before attempting to strip the LLC header. Previously, if bytesread < LLC_LEN, the code would perform stream_write(..., bytesread - LLC_LEN) which could result in a large negative value (integer underflow) and potential buffer overflow.
• ospfd/ospf_ext.c: Corrected three instances where TLV_DATA(&exti->prefix.header) and TLV_DATA(&exti->link.header) were changed to TLV_DATA(&exti->prefix) and TLV_DATA(&exti->link). While functionally equivalent (since header is the first struct field), passing the full struct address is clearer for static analysis tools and prevents false buffer overflow warnings.

Confidence Score: 5/5

• This PR is safe to merge with no concerns
• All changes are focused Coverity static analysis fixes with no functional behavior changes (except fixing an actual security vulnerability). The IS-IS fix addresses a real buffer underflow issue, while the BGP and OSPF changes improve code clarity for static analysis without altering runtime behavior.
• No files require special attention

Important Files Changed

Filename	Overview
bgpd/bgpd.c	Added Coverity annotations to suppress false positive memory leak warnings for clearing batch management
isisd/isis_pfpacket.c	Fixed potential buffer underflow by validating packet size before LLC header removal
ospfd/ospf_ext.c	Corrected TLV_DATA macro usage to pass full struct address instead of nested header field, preventing static analysis false positives

_{Last reviewed commit: 2b84aa6}

[riw777]

looks good