security/suricata: Fix libpcap LIB_DEPENDS

Fix the PORTS_PCAP option LIB_DEPENDS entry ambiguously depending on
net/libpcap, which should be libpcap.so.1 so as not to be satisfied
with the pcap library provided by base. [1]

While I'm here:

• Explicitly BUILD_DEPEND on libhtp >= 0.5.20, as configure breaks when that minimum version is not available.

PR: 211578
Reported by: marino [1]