This context must be set for TX buffers, and there's no better place to
set it than at the allocation time. If not set, it may end up NULL,
causing adverse effects (one seen by few parties is dereferencing random
memory locations to get (random again) MSS values). For RX buffers, uIP
context is set elsewhere too, but anyway, common sense says that if a
buffer is allocated for network context X, and that context uses uIP
connection Y, the a buffer should be just cross-linked with Y during
allocation time, not somewhere later.
Change-Id: Icdb3cd724802ca263c1cd0e3909be811e53822ba
Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>