docs: networking: Describe irq suspension

Describe irq suspension, the epoll ioctls, and the tradeoffs of using
different gro_flush_timeout values.

Signed-off-by: Joe Damato <jdamato@fastly.com>
Co-developed-by: Martin Karsten <mkarsten@uwaterloo.ca>
Signed-off-by: Martin Karsten <mkarsten@uwaterloo.ca>
Reviewed-by: Sridhar Samudrala <sridhar.samudrala@intel.com>
Reviewed-by: Bagas Sanjaya <bagasdotme@gmail.com>
Link: https://patch.msgid.link/20241109050245.191288-7-jdamato@fastly.com


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