lorawan: services: swap `select` to `depends on`

Switch the selects on `LORAWAN_FRAG_TRANSPORT` to `depends on`. `select`
should only be used for simple symbols without dependencies themselves.
Mixing `depends on X` and `select X` on different symbols is the primary
cause of Kconfig dependency loops.

Signed-off-by: Jordan Yates <jordan@embeint.com>