compat: Backport IPv4 reassembly.

compat: Backport IPv4 reassembly.

Backport IPv4 reassembly from the upstream commit caaecdd3d3f8 ("inet:
frags: remove INET_FRAG_EVICTED and use list_evictor for the test").

This is necessary because kernels prior to upstream commit d6b915e29f4a
("ip_fragment: don't forward defragmented DF packet") would not always
track the maximum received unit size during ip_defrag(). Without the
MRU, refragmentation cannot occur so reassembled packets are dropped.

Signed-off-by: Joe Stringer <joestringer@nicira.com>
Acked-by: Pravin B Shelar <pshelar@nicira.com>