tools: import tunslip from contiki

dist/tools/tunslip/.gitignore

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+tapslip6
+tunslip
+tunslip6

dist/tools/tunslip/Makefile

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+PREFIX ?= /usr/local
+BIN    = tapslip6 tunslip tunslip6
+
+all: $(BIN)
+
+install:
+	mkdir -p $(PREFIX)/bin && install $(BIN) $(PREFIX)/bin
+
+uninstall:
+	rm -f $(foreach bin,$(BIN),$(PREFIX)/bin/$(bin))

dist/tools/tunslip/README.md

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+Creating a SLIP network interface
+=================================
+
+The module `ng_slip` (Serial line IP) enables the RIOT network stack to
+communicate IP packets over the serial interface. This collection of tools
+originally from Contiki [1] enables Linux to interpret this data. Though there
+is a tool for such operations on Linux (`slattach`) it is only able to handle
+IPv4 packages and is unnessarily complicated.
+
+# Installation
+Just install them using
+
+``` {.sh}
+make
+sudo make install
+```
+
+By default they are installed to the `/usr/local/bin` directory, you can however
+change that by setting the PREFIX environment variable
+
+``` {.sh}
+export PREFIX=${HOME}/.local
+make
+sudo make install
+```
+
+# Usage
+`tapslip6` allows you to open a TAP interface (includes link-layer data) for
+a serial interace handling IPv6 data,
+`tunslip` allows you to open a TUN interface (includes only network-layer data)
+for a serial interace handling IPv4 data, and
+`tunslip6` allows you to open a TUN interface (includes only network-layer data)
+for a serial interace handling IPv6 data.
+
+For more information use the help feature of the tools
+
+``` {.sh}
+tapslip -h
+tunslip -h
+tunslip6 -h
+```
+
+[1] https://github.com/contiki-os/contiki/tree/a4206273a5a491949f9e565e343f31908173c998/tools