tcp: rename inet_csk_{delete|reset}_keepalive_timer()

inet_csk_delete_keepalive_timer() and inet_csk_reset_keepalive_timer()
are only used from core TCP, there is no need to export them.

Replace their prefix by tcp.

Move them to net/ipv4/tcp_timer.c and make tcp_delete_keepalive_timer()
static.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Jason Xing <kerneljasonxing@gmail.com>
Reviewed-by: Joe Damato <jdamato@fastly.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://patch.msgid.link/20250206094605.2694118-1-edumazet@google.com


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