sfc: Document current usage of efx_rx_buffer::len and efx_nic::rx_buffer_len
sfc: Document current usage of efx_rx_buffer::len and efx_nic::rx_buffer_len

Signed-off-by: Ben Hutchings <0672176982fbc629cc374f31a7a45ae1671abf90@solarflare.com>

TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas