use-of-uninitialized values in print-esp.c

[fxlb]

Need to fix print-esp.c. Test case:

$ CC=clang CFLAGS='-fno-omit-frame-pointer -fsanitize=memory -fno-optimize-sibling-calls -fPIC -g3 -ggdb3 -O0' ./configure

$ make -s clean all

$ ./tcpdump -#n -E "file tests/esp-secrets.txt" -r tests/espudp1.pcap

1) tcpdump-4.9 branch:

reading from file tests/espudp1.pcap, link-type EN10MB (Ethernet)
==205441==WARNING: MemorySanitizer: use-of-uninitialized-value
#0 0x5e74f5 in esp_print
...

[fxlb]

Workaround commited.