tcp: add const to tcp_try_rmem_schedule() and sk_rmem_schedule() skb

These functions to not modify the skb, add a const qualifier.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20250711114006.480026-7-edumazet@google.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>