ip-route: Fix nexthop encap parsing

ip-route: Fix nexthop encap parsing

When parsing nexthop parameters, a buffer of 4k bytes is provided. Yet,
in lwt_parse_encap() and some functions called by it, buffer size was
assumed to be 1k despite the actual size was provided. This led to
spurious buffer size errors if the buffer was filled by previous nexthop
parameters to exceed that 1k boundary.

Fixes: 1e5293056a02c ("lwtunnel: Add encapsulation support to ip route")
Fixes: 5866bddd9aa9e ("ila: Add support for ILA lwtunnels")
Fixes: ed67f83806538 ("ila: Support for checksum neutral translation")
Fixes: 86905c8f057c0 ("ila: support for configuring identifier and hook types")
Fixes: b15f440e78373 ("lwt: BPF support for LWT")
Signed-off-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>