CVE-2026-72413: sctp: fix err_chunk memory leaks in INIT handling

In the Linux kernel, the following vulnerability has been resolved:

sctp: fix errchunk memory leaks in INIT handling

When sctpverifyinit() encounters unrecognized parameters, it allocates an errchunk to report them. However, this chunk is leaked in several code paths:

1. In sctpsfdo51Binit(), if securitysctpassocrequest() fails after sctpverifyinit() has populated errchunk, the function returns immediately without freeing it.

2. In sctpsfdounexpectedinit(), the same leak occurs on the securitysctpassocrequest() failure path.

3. In sctpsfdounexpectedinit(), on the success path after copying unrecognized parameters to the INIT-ACK, the function returns without freeing errchunk, unlike sctpsfdo51Binit() which properly frees it.

Fix all three leaks by adding sctpchunkfree(errchunk) calls before returning in the error paths and on the success path in sctpsfdounexpectedinit().