link/sit: Add missing prototype for rtnl_link_is_sit()
link/sit: Add missing prototype for rtnl_link_is_sit()

Add the function prototype for rtnl_link_is_ipip() to the public header.

This fixes the following GCC warning when compiling with
-Wmissing-prototypes:

  route/link/sit.c:400:5: warning: no previous prototype for ‘rtnl_link_is_sit’ [-Wmissing-prototypes]

Signed-off-by: Tobias Klauser <9249c549618448e4c699e8032ba6c7f0d7fd4b7f@distanz.ch>

HolyShitMan/libnl-1,HolyShitMan/libnl-1,thom311/libnl,HolyShitMan/libnl-1,dsahern/libnl,dsahern/libnl,tklauser/libnl,greearb/libnl-ct,greearb/libnl-ct,dsahern/libnl,HolyShitMan/libnl-1,tklauser/libnl,thom311/libnl,tklauser/libnl,thom311/libnl,tklauser/libnl,greearb/libnl-ct,dsahern/libnl