Replace strlcpy() with memcpy() since the source buffer is not a string.
strlcpy() caught this anyway, but memcpy() usage is probably more valid.
==29766==WARNING: MemorySanitizer: use-of-uninitialized-value
#0 0x562bc2e50420 in strlcpy /home/mbr/git/fwknop.git/common/strlcpy.c:61:3
#1 0x562bc2e25362 in process_packet /home/mbr/git/fwknop.git/server/process_packet.c:225:5
#2 0x7fa6173c9d57 (/lib64/libpcap.so.1+0x1fd57)
#3 0x562bc2e2456a in pcap_capture /home/mbr/git/fwknop.git/server/pcap_capture.c:227:15
#4 0x562bc2e13ef0 in main /home/mbr/git/fwknop.git/server/fwknopd.c:296:13
#5 0x7fa61643724a in __libc_start_main /usr/src/debug/glibc-2.27-74-g68c1bf8097/csu/../csu/libc-start.c:308:16
#6 0x562bc2d9dec9 in _start (/home/mbr/git/fwknop.git/server/.libs/fwknopd+0x1dec9)
Uninitialized value was created by a heap allocation
#0 0x562bc2da6c84 in malloc (/home/mbr/git/fwknop.git/server/.libs/fwknopd+0x26c84)
#1 0x7fa6173ca996 (/lib64/libpcap.so.1+0x20996)
SUMMARY: MemorySanitizer: use-of-uninitialized-value /home/mbr/git/fwknop.git/common/strlcpy.c:61:3 in strlcpy