net: refactor tcp splice receive path to improve readability
net: refactor tcp splice receive path to improve readability

- move all of the details on offsets, lengths and buffers into a
single function instead of doing these operation from multiple places

- use a bottom up approach: try to avoid details in the high level
functions, introduce them gradually as we go deeper in the function
call stack

With helpful feedback from Jarek Poplawski.

Signed-off-by: Octavian Purdila <91308da0bf7e40e0a8ed5b7ced492510cbb48f46@ixiacom.com>
Acked-by: Jarek Poplawski <85e4e0cd35fdfcbe234be29b330d591ff9717625@gmail.com>
Signed-off-by: David S. Miller <fe08d3c717adf2ae63592e4c9aec6e3e404d8e3e@davemloft.net>

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