mptcp: mptcp_dss_len and mptcp_sched_rr can be static

It's used nowhere else except in this file.

(found with sparse static code analyzer)

Signed-off-by: Christoph Paasch <christoph.paasch@uclouvain.be>
Signed-off-by: Gregory Detal <gregory.detal@uclouvain.be>
mptcp: Add const qualifiers to functions in mptcp_input.c

It allows the compiler to optimize stuff.

Signed-off-by: Christoph Paasch <christoph.paasch@uclouvain.be>
Signed-off-by: Gregory Detal <gregory.detal@uclouvain.be>
mptcp: Cleanup __mptcp_find_free_index

Since 8ee987ac0ada7 (mptcp: Cleanup), __mptcp_find_free_index does not
take into account 'j' anymore as it is not used at all. This implied
that at the end of the loop-statement we added an immediate 'return'.

So, the loop will actually never loop at all. So, we can simply
clean it up by making a simple if statement, which makes it less
confusing.

Further, we can use a recursive call when we have gone beyond the bounds
of the bitfield. We just need to make sure that we do not loop through
these recursive calls. This is made sure by checking if bitfield ==
0xff. That way, if there are no bits free, we exit immediatly.

Finally, all of this code can be moved to mptcp_fullmesh.c, where it is
actually used.

(found by smatch, static code analyzer)

Signed-off-by: Christoph Paasch <christoph.paasch@uclouvain.be>
Signed-off-by: Gregory Detal <gregory.detal@uclouvain.be>