lib,sharpd,zebra: Extend nexthop_add_srv6_seg6 to encode encap behavior

lib,sharpd,zebra: Extend nexthop_add_srv6_seg6 to encode encap behavior

Previous commits introduced the `encap_behavior` field in the SRv6
nexthop data structure and updated the compare, hash, and copy
functions to handle this new field.

This commit extends the `nexthop_add_srv6_seg6` function by adding a
new parameter `encap_behavior` and modify the code in various places
to pass the encap behavior when calling this function.

Signed-off-by: Carmine Scarpitta <cscarpit@cisco.com>