[nrf toup][nrfconnect] Added BT reassembly config to BT SMP samples

[HubertHugo]

This PR adds BT reassembly config to SMP DFU samples as it is recommended

[NordicBuilder]

none

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[markaj-nordic]

Maybe it's better to first add it to upstream and then pull in as [nrf fromtree.]

[HubertHugo]

Maybe it's better to first add it to upstream and then pull in as [nrf fromtree.]

@markaj-nordic I don't know what are pluses and minuses of this approach so I can change it if you guys agree on that.

[markaj-nordic]

Maybe it's better to first add it to upstream and then pull in as [nrf fromtree.]

@markaj-nordic I don't know what are pluses and minuses of this approach so I can change it if you guys agree on that.

For me the rule of thumb for [toup] is the need of urgent patch/fix in our SDK. This change is just a minor improvement, so I'd suggest to go upmerge first. On the other hand, it's just our platform being affected, so I maybe I'm too picky.