Currently, when hb_interval is changed by users, it won't take effect
until the next expiry of hb timer. As the default value is 30s, users
have to wait up to 30s to wait its hb_interval update to work.

This becomes pretty bad in containers where a much smaller value is
usually set on hb_interval. This patch improves it by resetting the
hb timer immediately once the value of hb_interval is updated by users.

Note that we don't address the already existing 'problem' when sending
a heartbeat 'on demand' if one hb has just been sent(from the timer)
mentioned in:

  https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg590224.htmlSigned-off-by: Xin Long <lucien.xin@gmail.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Link: https://lore.kernel.org/r/75465785f8ee5df2fb3acdca9b8fafdc18984098.1696172660.git.lucien.xin@gmail.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>