www/kannel: Unbreak build with GCC 10 (-fno-common default)

/usr/local/bin/ld: libwap.a(wtp_resp.o):(.bss+0x8): multiple definition of `dispatch_to_wsp'; libgw.a(wap_push_ota.o):(.bss+0x8): first defined here

http://package18.nyi.freebsd.org/data/121amd64-default-PR244494/2020-06-10_18h04m44s/logs/errors/kannel-1.4.4_9,1.log

PR: 246700