Apply partial loop-unrolling to avoid trace aborts

The JIT compiler has to unroll inner loops in a trace.  It does this
up to a (configurable) limit and aborts the trace if it hits that
limit.

This commit tries to avoid excessive unroll operations by manually
unrolling a few iterations in critical code sections like multi-buffer
receive and transmit processing.  This significantly reduces trace
aborts in the case of, for example, encapsulation operations that
typically use two buffers per packet.  It should not have any negative
impact on single-buffer packets.

The commit also includes a few deliberate preventions of tailcalls to
avoid an effect discussed in the thread at
http://www.freelists.org/post/luajit/FFI-methods-for-userdata-objects,3
Intel10g: set and reset rates and priority
Don't complain for reusing when the set is totally full; only complain if you need an extra slot
Intel10G: MPSAR holds 0..255 and not 0..127
Merge pull request #243 from javierguerragiraldez/full_state

Intel10G: bugfixes that arise when all app slots are used
Merge pull request #238 from alexandergall/loop-unroll

Apply partial loop-unrolling to avoid trace aborts
Merge pull request #239 from javierguerragiraldez/priority

Intel10g: set and reset rates and priority
Merge pull request #244 from javierguerragiraldez/master

lib.pcap.lua: replace ffi.cast() from a local string with ffi.copy()