MFC: Make interrupt pipe interval time configurable.
- Add kernel options: {UPLCOM,UVSCOM}_INTR_INTERVAL
- Add sysctl variables: 'hw.usb.{uplcom,uvscom}.interval'
sys/conf/options: 1.426
sys/dev/usb/uplcom.c: 1.16
sys/dev/usb/uvscom.c: 1.19
sys/i386/conf/LINT: 1.1189 (in NOTES)
sys/modules/uplcom/Makefile: 1.2