CVE-2026-64577 gtp: check skb_pull_data() return in gtp1u_send_echo_resp()

In the Linux kernel, the following vulnerability has been resolved: gtp: check skbpulldata return in gtp1usendechoresp gtp1usendechoresp ignores skbpulldata's return value. Its caller gtp1uudpencaprecv only guarantees 16 bytes udphdr + gtp1header, but the pull requests 20 gtp1headerlong + udphdr...